FR:

Une gamme de coûts probables pour l’eau potable distribuée par la ville de Québec, Canada, est déterminée en sommant les coûts annualisés des investissements nécessaires à la reconstruction à l’état neuf des infrastructures d’eau de la ville (conduites d’aqueduc et d’égout, stations de production d’eau potable et stations de traitement des eaux usées) et les coûts annuels d’opération et d’entretien associés à ces infrastructures, puis en divisant le coût total par la production annuelle moyenne d’eau potable sur le territoire de la ville de Québec (106 Mm³/an). La gamme de coûts est obtenue par 50 000 simulations Monte Carlo, en tenant compte des incertitudes sur le coût des divers éléments composant le coût total de l’eau. De cette façon, on calcule un coût total moyen de 2,85 $/m³ et d’écart-type 0,47 $/m³. Globalement, 0,70 $/m³ et 2,15 $/m³ sont respectivement liés, en moyenne, aux coûts d’exploitation et aux dépenses d’immobilisation. Une analyse de sensibilité des résultats montre que le taux d’intérêt et le coût de construction des conduites sont les paramètres ayant le plus d’impact sur le coût calculé. Ce coût s’avère d’ailleurs beaucoup plus élevé que le prix moyen chargé pour l’eau au Canada et au Québec, qui était respectivement de 1,00 $/m³ et 0,49 $/m³ en 1999, mais s’approche du prix moyen chargé en France pour l’eau potable en 2000 (environ 3,33 $/m³ hors taxes), pays où la facture d’eau inclut l’intégralité des dépenses des services d’eau et d’assainissement. La récupération par les municipalités, sous quelle forme que ce soit, de 2,85 $ pour chaque m³ d’eau produit permettrait d’assurer un entretien et un renouvellement adéquats des infrastructures d’eau municipales.

EN:

Canadians are among the greatest water consumers in the world with a mean commercial and domestic consumption of 444 litres per person per day (L/p/d). As a comparison, the mean urban consumption in France is 210/p/d. Since water sources are abundant and apparently cheap in Canada, most people don’t make any effort to reduce their water consumption. However, even though raw water is a free public good, potable water production and distribution as well as wastewater collection and treatment require important operating and investment costs. Major investments will also be required during the coming years in many Canadian municipalities in order to restore water and sewer pipes and to update or, in some cases, build new treatment plants. Potable water delivered by municipalities thus has a cost, and this cost is estimated for Quebec City, Canada, in this paper.

The scientific literature only gives a few assessment examples of the real cost of potable water delivered by municipalities. Some authors present general methodologies to estimate the cost of each cubic meter produced, based on the definition of fixed and variable costs (e.g., CABRERA et al., 2003; MCNEIL and TATE, 1991), but application results for these methodologies cannot be found. In 2001, the American Water Works Association (AWWA) compiled revenue and financial data linked to drinking water for 647 American and 24 Canadian municipalities (AMERICAN WATER WORKS ASSOCIATION, 2001). However, this database does not include sanitation costs (wastewater collection and treatment). In November 2002, PricewaterhouseCoopers determined that the total costs for potable water and wastewater in Montreal were $0.54/m³ in 2000 and would reach $0.83/m³ in 2022 (PRICEWATERHOUSECOOPERS, 2002). But this estimate did not include assets that were already paid, and thus underestimated the real cost of potable water. Since many North American municipal water infrastructures are aging and will need to be replaced and/or rehabilitated soon, it is essential to include the cost of all infrastructure (water pipes and sewer networks, drinking water and wastewater treatment plants) when estimating the cost of water.

In the province of Quebec, water services are, in most cases, under the responsibility of the municipalities. Depending on the city, the water services are financed directly from the property tax or from a specific pricing method (flat rate or volume-based).

The total cost associated with drinking water is the sum of investment, operation, maintenance and repair costs for potable water production and distribution, as well as for wastewater collection and treatment. The first step for the calculation of this cost was to estimate the construction costs of the equipment needed to perform all of these functions. As a case study, we computed the financial resources required to reconstruct Quebec City’s equipment and networks, as they existed in 2002. This reconstruction cost was annualized according to the life expectancy of each piece of equipment. As a second step, the annualized reconstruction cost was added to the annual operation, maintenance and repair costs. The total annual cost was then divided by the mean annual water production in the Quebec City region, to obtain the total potable water volumetric cost. All costs presented in this paper are in 2002 Canadian dollars, using the seasonally adjusted Statistics Canada Consumer Price Index (CPI). To take into account the uncertainty associated with the parameters used to compute the water cost, normal distributions were assigned to these parameters and the total water cost was assessed from 50,000 Monte Carlo simulations. A variance analysis was also performed to determine the impact of each parameter on the computed cost for water.

The case study selected to compute the total water cost is the new city of Quebec, as incorporated on January 1^st, 2002. The municipalities of Saint-Augustin and l’Ancienne-Lorette were also taken into consideration in the calculation, since these two cities use Quebec City equipment for potable water supply and wastewater treatment. In 2001, the total population of this region was 508,000 inhabitants and the total drinking water production was estimated at 287,882 m³/day (Table 2). The total length of drinking water pipes in this case study is 2,453 km and the sewer total length is 4,133 km (Table 3). In 2002, there were two wastewater treatment plants and three drinking water treatment plants in the region of this case study; the city plans to entirely renovate one of the drinking water treatment plants and to build one new plant next year. The costs and construction years of Quebec’s stations are presented in Table 4. The statistical distributions of all the parameters used to compute the water cost are summarized in Table 1.

The 50,000 Monte Carlo simulations led to a mean total cost of $2.85/m³ for water in Quebec City, with a standard deviation of $0.47/m³. This means that the total cost of water has a 95% chance to lie between $1.91/m³ and $3.80/m³ in Quebec. On average, the investment cost represents $2.15/m³ and the maintenance, operation and repair cost is $0.70/m³. The distribution of the total estimated cost is illustrated in Figure 1. Table 5 summarizes the statistical characteristics obtained for the components of the total water cost.

The computed cost is much higher than the average price paid by Canadians and Quebecers for their potable water, which was respectively $1.00/m³ and $0.49/m³ in 1999. However, the calculated cost is close to the average price charged for potable water in France in 2000 (about $4.24/m³ including taxes, which means $3.33/m³ without taxes), a country where all costs related to drinking water and wastewater are included in the water bill. Proper maintenance and renewal of municipal water infrastructures would be ensured if cities were to recover $2.85 for each m³ of water produced, in one way or another. Moreover, it should be noted that water meter installation, especially for industrial and commercial users, would become economically beneficial if the exact water cost were to be charged to consumers.

FR:

La rivière Yamaska est l’un des affluents du Saint-Laurent les plus contaminés par les activités agricoles. Cette problématique touche particulièrement le sous-bassin de la rivière Noire où les dépôts de surface du Quaternaire sont discontinus, de faible épaisseur et souvent perméables. L’objectif de cette étude est de déterminer la vulnérabilité de l’eau souterraine sur une partie du sous-bassin de la rivière Noire (100 km²). La méthodologie utilisée comprend la caractérisation de l’aquifère, l’analyse des concentrations en nitrates et des contenus en δ¹⁸O, l’étude de la vulnérabilité en utilisant l’approche AQUIPRO et la modélisation hydrogéologique. Les résultats montrent une dégradation significative et d’origine anthropique de l’eau souterraine : plusieurs concentrations excèdent 1 mg N-NO₃/L et quelques-unes excèdent 10 mg N-NO₃/L. Les puits contaminés sont situés sur les crêtes topographiques où le silt argileux est absent et le till discontinu, et où la plus grande vulnérabilité AQUIPRO a été identifiée. Une diminution des concentrations avec la profondeur de prélèvement s’explique par un écoulement souterrain peu profond entraînant les nitrates vers un ruisseau et vers la rivière Noire. La vulnérabilité de l’eau souterraine est ainsi beaucoup plus grande dans les couches superficielles du roc fracturé. Le temps moyen de séjour de l’eau souterraine est estimé à 20 ans. Les concentrations mesurées permettent d’établir un lien direct entre la vulnérabilité, les dépôts de surface, la stratigraphie du substrat et les directions de l’écoulement souterrain. Elles démontrent aussi la présence d’une contamination de l’eau souterraine par les nitrates qui est susceptible d’augmenter si aucune mesure préventive n’est mise en place.

EN:

Many studies have shown a link between intensive agricultural practices and groundwater pollution by nitrates. In Québec, recent studies have shown that the Yamaska River is highly contaminated by agricultural activities. Maize and pork production are particularly intensive in the Noire River sub-basin. In this area, quaternary deposits are discontinuous, of limited thickness and are generally permeable, leading to high groundwater vulnerability. The objective of this study was to determine groundwater vulnerability to nitrate contamination on a small agricultural sub-watershed of the Noire River. The methodology included aquifer characterization, analysis of nitrate concentrations and δ¹⁸O composition, as well as a vulnerability evaluation and groundwater flow modelling.

Located on the south shore of the Saint Lawrence River, the Noire River (1579 km²) is located in the southeastern portion of the Yamaska basin. A small part of the basin (100 km²) was the focus of this study. The Noire River flows in the centre of the study area whereas the Aulnages creek is a small tributary to the Noire River. The study area was limited to the east and west by topographic highs. It is located between the limit of the St. Lawrence Lowlands and the first Appalachian ridges. The bedrock, Cambrian to Ordovician in age, is mainly made of limestone in the western zone and is composed of terrigenous siliciclastic facies in the eastern zone. The substratum forms elongated crests, due to the tectonic grain, surrounded by recent surface deposits. These quaternary deposits are discontinuous and are of limited thickness. The hydrological potential of the fractured rock aquifer is interesting but spatially variable.

The deposits were analyzed at 50 observation sites and 18 typical samples were sieved or submitted for density analysis (GEOTERAP). Data from the Système d’Information Hydrogéologique (SIH) were used to complete the field information in establishing the stratigraphy of the area. Soil hydraulic conductivity was measured using a Guelph permeameter and two short-term pumping tests were performed. Monthly water levels were measured in 18 private wells from June 2001 to June 2002. Water was sampled bimonthly from 35 sites (25 deep wells, two shallow wells, two sites in the Noire River, four in the Aulnages stream, and two in a temporary lake, located in a gravel pit). In October 2001 and April 2002, water was sampled for δ¹⁸O composition. Analyses were performed at the GÉOTOP-UQÀM-McGill laboratories. Aquifer vulnerability was determined using the AQUIPRO approach, a simple method that considers clay and till thickness, in addition to well depth. A groundwater flow model was developed using MODFLOW and MODPATH to simulate groundwater flow, flow paths and residence times.

Characterization of the quaternary deposits confirmed the following sequence, from the base to the top: till; clayey silts; sand and sandy gravel. The thickness of these deposits was variable, and there were bedrock outcrops, mainly on the western and eastern sides of the study area. A north-south esker (partially exploited) is present on the western side of the Noire River. Measured soil hydraulic conductivities show that the clayey silts and till deposits have low permeability whereas the sand is more permeable. Clayey silts present in the centre of the study area, as well as occasional till deposits, offer partial protection to the aquifer, whereas elsewhere infiltration and contaminants can reach the aquifer through recharge. Pumping tests showed high transmissivities for the rock formation, probably resulting from the important rock fracturing in the upper 10 to 15 m of the aquifer. Groundwater flowed towards the river from the eastern and western limits of the study area, and water depth was on average 2.5 m. The Noire River is generally in contact with rock and drains the aquifer.

Measured nitrate concentrations exceeded 10 mg  N‑NO₃/L (guideline for potable water) in the two sampled surface wells. Concentrations were between 1 and 10 mg N-NO₃/L at least once during the study period in ten of the 25 deep sampled wells, indicating a groundwater contamination problem of anthropogenic origin. The highest concentrations were measured in recharge areas and nitrate concentrations were found to decrease generally with well depth. Nitrate concentrations were higher in the Aulnages creek than in the Noire River, probably because the creek intercepts drainage water and shallow groundwater flow. The isotopic composition of surface wells, deep wells and Aulnages creek water remained relatively stable between sampling times. This indicates an important mixing of fresh recharge with in situ groundwater. In the Noire River, δ¹⁸O compositions reflect the yearly variations in precipitation.

AQUIPRO aquifer vulnerability was highest in the eastern and western parts of the study area where the highest nitrate concentrations were measured. AQUIPRO vulnerability was lowest where the clayey silts provide some protection near the Noire River. The results showed an important spatial heterogeneity in the thickness of the clayey silt layer, underlining the generally high aquifer vulnerability in the study region. The groundwater flow model developed using field data simulated the measured heads adequately. Flow directions simulated with MODPATH confirmed the presence of a shallow groundwater flow from the eastern and western limits and towards the Noire River. This flow is probably responsible for the decreasing nitrate concentrations observed with increasing water sampling depth and confirms that aquifer vulnerability varies with depth in the aquifer. The average groundwater residence time is 20 years. This means that recharge will take on average 20 years to travel through the aquifer and to the Noire River. It also indicates the time frame required for the aquifer to eliminate a large-scale nitrate contamination, after the initiation of control measures.

This work showed that groundwater nitrate contamination is related to groundwater vulnerability, which is a function of quaternary deposits, substrate stratigraphy and groundwater flow directions. These factors must be considered when studying groundwater vulnerability as they directly affect contaminant transport. It therefore appears necessary to use a combination of various approaches to better understand aquifer vulnerability and to design preventive measures. This work also demonstrated groundwater contamination by nitrates in the study region. Because of the generally high vulnerability of the aquifer, increased nitrate contamination can be expected in the future if no preventive measures are undertaken to protect the groundwater resource.

FR:

L’alimentation des eaux souterraines procède entre autres par des apports d’eau d’infiltration à travers les différents horizons du sol qui séparent la surface du sol du toit de la nappe phréatique. Une étude a été réalisée au laboratoire sur le rôle de la charge d’eau introduite dans une colonne de sol de 1 m de hauteur située au toit de la nappe, dans le transfert à l’eau souterraine, des bactéries indicatrices de pollution de l’eau de boisson. Les charges d’eaux usées de 50 mL, 100 mL et 250 mL ont été appliquées. Les analyses des eaux avant et après percolation ont concerné les coliformes thermotolérants et streptocoques fécaux, pour les paramètres bactériologiques, et le pH, NH₄⁺ et la conductivité électrique, pour les paramètres chimiques.

Les résultats révèlent une réduction du nombre de microorganismes dans les eaux qui ont percolé à travers la colonne du sol. Cette réduction est imputable à la rétention de ces cellules par la colonne de sol. À la charge de 50 mL d’eau appliquée au-dessus de la colonne du sol, cette réduction a été de l’ordre de 7 unités logarithmiques pour les coliformes thermotolérants, et de 6 pour les streptocoques fécaux. En appliquant la charge de 250 mL, la réduction a plutôt été de l’ordre de 6 unités logarithmiques pour les coliformes thermotolérants, et de 7 pour les streptocoques fécaux. Cette réduction de la concentration microbienne circulante observée dans les eaux percolées a été de l’ordre de 7 unités logarithmiques pour les deux groupes de bactéries lorsque la charge de 100 mL a été appliquée. À charge d’eau usée élevée, la colonne de sol semble ainsi retenir plus de streptocoques fécaux que de coliformes thermotolérants. Ce comportement de la colonne de sol semble s’inverser lorsque la charge d’eau appliquée est relativement faible. Les éléments chimiques sont également retenus par le sol. Les caractéristiques des eaux qui percolent évoluent dans le temps, montrant que la rétention des polluants des eaux d’infiltration par une colonne de sol est un processus dynamique.

EN:

Water percolation through different soil horizons is one of the main mechanisms contributing to the improvement of the microbial quality of ground water. These soil horizons separate the soil surface from the groundwater table. Wastewater often contains chemicals and microbial pollutants, generally at high concentrations. On the other hand, ground water constitutes a major natural resource in most regions of the world. The present study was carried to examine the transfer of bacterial pollutants to the ground water, with the objective of evaluating the influence of the rate at which wastewater percolates through a soil column overlying the groundwater table.

The soil column was 25 cm in diameter and one meter high. It was composed of two horizons of different heights with pH values that varied from 4.43 to 4.56. Wastewater percolation tests were carried out with volumes of 50 mL, 100 mL and 250 mL, which were introduced every 30 minutes for each experiment. Chemical analysis was performed for pH, NH₄⁺ and electrical conductivity. Bacteriological analysis was also carried out for thermo-tolerant coliforms and faecal streptococci quantification. These analyses were first carried out on each wastewater sample before introduction into the soil column, and then again after their percolation through the soil column.

Results showed that the lapse of time needed to observe the first percolated water drop was longer for low water loads than for the higher water loading rates. On the other hand, the time necessary to collect an adequate volume of percolated water for analysis was shorter for low water loads than for the high water loads. The average volume of percolated water per hour was thus high at low water loads, and relatively low at high water loading rates.

A comparison of the microbial characteristics of the introduced wastewater and those of the percolated water showed that the bacterial load in the percolated water was lower. This reduction was due to bacterial retention by the soil column. At an applied load of 50 mL, this reduction was of the order of 7 log units for thermo-tolerant coliforms, and 6 log units for faecal streptococci. When water load of 250 mL was applied, the reduction was of the order of 6 log units for thermo-tolerant coliforms, and 7 log units for faecal streptococci. The reduction was in order of 7 log units for both bacterial groups at an applied wastewater loading of 100 mL. It thus appears that, at high applied wastewater loadings, the soil column retained faecal streptococci better than thermo-tolerant coliforms. The soil column behaviour was reversed when low wastewater loads were applied. It was also noted that for electrical conductivity, a reduction varying from 6,240 to 6,550 µS/cm was obtained in the water leaving the soil column. The concentration of ammonia decreased from 44‑50 mg/L at the entrance to the column to around 1 mg/L at the exit of the column. Average pH values of water percolated through the two soil horizons varied from 5.70 to 7.32, whereas pH values of water introduced into the soil column varied from 7.43 to 8.02. It thus appears that the pH of these two soil horizons strongly influenced the pH of the percolating water that would enter the underlying ground water. The chemical and bacteriological characteristics of percolating water exhibited temporal variations, showing that the retention of pollutants by the soil column was a dynamic process.

EN:

The aims of this work were to study, for the first time, the succession of microbial communities (from viruses to ciliates) in the largest occidental European lake (Lake Geneva) and to perform two one-week in situ experiments in March-April (Exp1) and May (Exp2) 2004 in order to assess both small flagellate protozoan and virus-induced mortality of heterotrophic bacteria. Both nanoflagellates and viruses could be responsible for 31 to 42% of the total daily mortality of heterotrophic bacteria. In May (Exp2), viruses could explain up to 10% of the bacterial mortality whereas flagellates were responsible for 32% of the bacterioplankton removal. These results provide new evidence for the critical role played by viruses in the functioning of the microbial food webs and highlight the importance of further considering this biological compartment for a better understanding of the plankton ecology of Lake Geneva.

FR:

Il est aujourd’hui bien établi que l’on ne peut prétendre comprendre le rôle du vivant dans le fonctionnement des écosystèmes aquatiques sans répondre à un certain nombre de questions fondamentales telles que celles portant sur l’identité et l’abondance des organismes présents, leurs taux métaboliques et reproductifs, ou encore leurs fonctions précises dans l’écosystème. Dans les systèmes lacustres, l’omniprésence et le rôle-clé des processus microbiens ont été largement démontrés au cours des deux dernières décennies. Toutefois, les mécanismes de régulation ainsi que la diversité fonctionnelle des communautés microbiennes demeurent un sujet central de la recherche actuelle. Si nous avons commencé à accumuler de grandes quantités d’informations concernant le compartiment bactérien, il n’en est pas de même pour le compartiment contenant les plus petites et les plus abondantes entités biologiques de la colonne d’eau : les virus. L’importance qualitative, quantitative et fonctionnelle des virus bactériophages et leur impact dans le contrôle et le déclin des communautés bactériennes dans les écosystèmes lacustres sont en effet encore mal connus. On sait aujourd’hui que les virus interviennent dans les processus de perte (mortalité) qui affectent les communautés microbiennes, mais aussi dans la structure en taille, la composition et la régulation de la diversité des peuplements microbiens, dans le recyclage des nutriments inorganiques et de la redistribution de la matière organique.

Dans ce travail, nous avons étudié, pour la première fois, la dynamique des communautés microbiennes dans le plus grand lac naturel d’Europe occidental (le lac Léman) entre février et juin 2004. Le dénombrement des différents micro-organismes (effectué à huit profondeurs comprises entre 0 et 50 m) a été obtenu via la cytométyrie en flux et la microscopie à épifluorescence. Cette approche « écosystémique » nous a permis d’acquérir une image aussi précise que possible de la structure et de la dynamique de la communauté microbienne, composée des picocyanobactéries, des bactéries hétérotrophes, de petits eucaryotes flagellés et ciliés hétérotrophes et mixotrophes et enfin des virus. Typiquement, il a pu être mis en évidence des liens étroits entre certaines communautés, comme par exemple les bactéries et les virus du groupe VLP1 (r = 0,51; p < 0,05; n = 72), suggérés être, pour l’essentiel, représentatifs de la communauté des bactériophages.

Parallèlement au suivi limnologique des communautés, une approche expérimentale in situ, à différentes périodes de l’année, a aussi été utilisée, afin d’estimer la part relative de la prédation par les protozoaires flagellés et de l’impact des virus sur la mortalité bactérienne. La méthode mise en application ici est dérivée de la technique de dilution initialement proposée pour évaluer l’impact du broutage des organismes zooplanctoniques sur le phytoplancton. Un échantillon intégré entre 0 et 10 m de la colonne d’eau a été pré-filtré sur 100 µm puis 11 µm pour ne conserver que les communautés virales, bactériennes et protistes flagellés, soumises alors à des dilutions successives en présence (eau filtrée sur 0,2 µm) ou absence (eau ultrafiltrée sur 100 kDa) de la communauté des virus.

Ces expériences, réalisées en microcosmes de 0,5 litre, ont été conduites en mars - avril (Exp1) et en mai (Exp2) 2004. Nos résultats ont révélé que les nanoflagellés et les virus étaient responsables ensemble de 31 à 42 % de la mortalité bactérienne journalière. En mai, les virus expliquaient à eux seuls 10 % de la mortalité bactérienne, et les nanoflagellés 32 %. Ces données suggèrent que la lyse virale peut induire des changements dans l’importance relative des groupes fonctionnels de la chaîne alimentaire et qu’elle est d’une importance significative sur la mortalité du bactérioplancton.

Les expériences en microcosmes ont également permis de détecter une population virale VLP4, discriminable par cytométrie en flux des autres communautés de par ses caractéristiques de taille et de fluorescence. L’analyse précise des abondances de ce groupe et des autres communautés nous a alors permis de montrer une relation étroite entre les abondances des VLP4 et de petits eucaryotes pigmentés (r = 0,38; p < 0,05; n = 58), suggérant que ce groupe de virus pouvait être spécifique de ces cellules autotrophes.

L’ensemble des résultats acquis met en évidence l’importance des virus dans le fonctionnement du réseau trophique microbien et la nécessité de considérer désormais ce compartiment biologique pour mieux comprendre l’écologie planctonique du Léman.

FR:

L’eau que nous consommons chaque jour est essentielle à la vie. Sa qualité a toujours été un élément indispensable à un environnement favorable à la santé. Actuellement, loin d’avoir été résolu, le problème de la qualité de l’eau de boisson est toujours une priorité de santé publique, autant dans les pays en voie de développement que dans les pays industrialisés.

Ce texte présente six défis pour la santé publique dans le dossier de l’eau potable pour les années futures :

1. L’utilisation d’une approche multibarrière dans la production et la distribution de l’eau potable, qui inclut la protection des sources d’eau, l’utilisation d’un traitement efficace, la qualité du réseau de distribution, la surveillance de la qualité de l’eau et la réponse lors d’un problème;

2. La mise au point de meilleures normes de qualité d’eau par le choix d’indicateurs plus pertinents, l’utilisation de méthodes d’analyse de risque plus adaptées, le suivi de la qualité de l’eau plus fréquent à être fait au robinet du consommateur;

3. L’amélioration de la surveillance des maladies d’origine hydrique ainsi que des méthodes d’investigation des épidémies;

4. L’amélioration des liens avec la communauté;

5. La prise en compte de critères de gestion transparents qui incluent l’accessibilité, l’équité, et les analyses coûts-bénéfices;

6. Le développement de la recherche sur les maladies d’origine hydrique, en particulier sur l’exposition réelle des populations aux contaminants de l’eau et l’évaluation des effets de la contamination de l’eau sur la santé.

Finalement, le problème de la qualité de l’eau potable doit être appréhendé dans une perspective mondiale.

EN:

Drinking water is essential to human life. Drinking water quality has always been an essential component of a healthy environment. In fact, the risk of waterborne diseases, either from microbiological or chemical contamination of drinking water, is still ubiquitous in both industrialized and non-industrialized countries. Recently, several outbreaks of waterborne enteritis in North America have confirmed the presence of this risk, with some potentially dramatic consequences such as the case that occurred in Walkerton, Ontario. Vulnerable people such as infants, pregnant women, senior citizens and individuals with compromised immune systems are particularly at risk. Other factors such as travel, migration, climate change, and intensive agriculture might increase the risk of emerging diseases. The lack of basic measures of public health such as protection of sources of water, adequate water treatment, or surveillance of drinking water has also been underlined in recent epidemics. Multi-chemical contamination at very low doses by pharmaceuticals or disinfectant by-products is also an issue that public health practitioners must deal with. New technology enables us to detect chemicals that were not detectable a few years ago.

With respect to all these potential threats, this paper presents six major challenges in the area of drinking water that are considered by the author as a priority for public health:

1. Implementation of the multi-barrier approach is fundamental for the prevention of waterborne diseases. It includes the protection of drinking water sources from contamination, efficient water treatment in every community including those in remote areas, operation and maintenance with competent operators, good water quality within the entire distribution network, an adequate monitoring of drinking water using real-time surveillance when feasible, and finally, rapid responses to «red flags» which might be raised by all types of monitoring and surveillance.

2. Increasing the level of drinking water standards is also paramount. It includes the use of the most pertinent index of bacterial, viral and parasitic contamination during water monitoring. This is also true for chemicals, where a global index of health risk should be developed. The use of the best risk-assessment methods when deriving standards is recommended, especially regarding the consideration of exposure through inhalation and dermal contact and the vulnerability of some sub-populations. An increase in the frequency of water quality monitoring is also recommended with sampling, when necessary, at the consumer’s tap.

3. Improving waterborne disease surveillance and methods of detection and investigation of outbreaks are still important. These are the public health watchdogs that are very useful when the previous measures have failed. They include the use of rapid and easy means of surveillance of acute enteric symptoms, such as monitoring diarrhoea medication sales, telephone calls received at a Health Line, or the monitoring of diarrhoea in some at-risk populations. Up-to-date methods to track pathogens in outbreak investigations would also be very useful to link diseases to water contamination.

4. Enhancing the links with communities is an important component of public health intervention. It includes annual reports to communities on water quality and involving citizens at the beginning of discussions when all important decisions regarding drinking water have to be made (e.g., upgrading a treatment plant). It might also be possible to inform a community when contaminants are found with concentrations that exceed 50% or less of the water quality standards.

5. Use of transparent and fair management criteria is a critical issue. Several standards have been driven mostly by the technical limitations of analytical methods and a low-cost approach. There are also potential threats that some minorities could have less access to water of good quality and suffer the burden of water contamination. The new management should include some important criteria as equity, social solidarity and valid cost-benefit analysis.

6. Developing research into human exposure and waterborne diseases epidemiology is the key issue to derive new knowledge to come up with the best water quality standards. It includes the use of efficient epidemiologic designs and a special focus on vulnerable populations (e.g., pregnant women, infants). Toxicological studies might still be useful if they improve risk assessment.

In conclusion, beyond traditional methods that have to be updated (multi-barriers, quality standards and surveillance of waterborne diseases and investigation of outbreaks), the new components of the public health approach in drinking water are: the quality of the link with the community, the use of transparent and fair criteria for risk management, and a strong research agenda focussing on human health impacts. Finally, the use of a global perspective is paramount. Most drinking water issues are spread worldwide and cooperation between nations and countries is an important component of a healthy world in this twenty-first century.

EN:

Comparisons of runoff and sediment loss from row-crop with and without riparian buffers, pasture and grass filter strips are limited. Effects of precipitation, landuse and buffer condition on runoff and sediment loss were examined from 1997 to 1999 in eight watersheds with varying proportions of row-crop, pasture, riparian buffers and grass filter strips. Runoff volume and sediment mass from row-crop watersheds were inversely related to the percentage of forest and pasture cover. Forest (n = 2), pasture (n = 3), row-crop (n = 2) and a row-crop watershed with grass filter strips (RC-GFS) had 3‑yr mean runoff of 939, 1,560, 3,434 and 1,175 m³ ha^‑1 yr^‑1, respectively. Runoff was greater from all landuses in a year when precipitation was 36% above normal (1998). The largest single runoff event from each watershed accounted for 11 to 25% of its total runoff. Forest, pasture, row-crop and RC-GFS watersheds lost 1,017, 1,241, 3,679 and 2,129 kg ha^‑1 yr^‑1 of sediment, respectively. In 1998, the RC-GFS watershed lost more sediment than row-crop watersheds and had less runoff and sediment loss in years with normal or below normal precipitation. Row-crop watersheds with 55% pasture reduced runoff and sediment loss by 55 and 66%, respectively, compared to row-crop watersheds. During 90% of the runoff events, more soil was lost from row-crop watersheds than pasture or forest watersheds. Results suggest that 3‑4 m grass filter strips, maintenance of 55% or more pasture/CRP land within row-crop watersheds and intact riparian buffers significantly reduce runoff and sediment losses from row-crop watersheds.

FR:

Les études comparant les volumes de ruissellement et les charges sédimentaires de bassins versants avec cultures en lignes et pâturages avec et sans zones tampons et bandes riveraines sont peu nombreuses. Les effets des précipitations, de l’occupation du sol et des conditions des zones tampons sur le ruissellement et les charges sédimentaires ont été analysés de 1997 à 1999 pour huit bassins versants comportant en proportions diverses des cultures en lignes, des pâturages, des zones tampons et des bandes riveraines. Il a été montré que les volumes de ruissellement et les charges sédimentaires pour les bassins versants avec cultures en lignes étaient inversement proportionnels aux pourcentages de forêt et de pâturages présents sur ces bassins. Les moyennes mesurées sur trois ans des volumes de ruissellement des bassins versants de type forestier, avec pâturages, avec cultures en lignes et avec cultures en lignes et bandes riveraines (RC‑GFS) sont de 939, 1 560, 3 434 et 1 175 m³/ha/an respectivement. Les volumes de ruissellement mesurés pendant une année pour toutes les occupations du territoire ont été plus grands lorsque les précipitations ont été supérieures de 36 % à la normale (1998). L’événement générant le volume de ruissellement le plus important à survenir sur chaque bassin versant génère à lui seul de 11 % à 25 % du volume de ruissellement total mesuré. Les charges sédimentaires pour les bassins versants forestiers, avec pâturages, avec cultures en lignes et RC‑GFS ont été respectivement de 1 017, 1 241, 3 679, et 2 129 kg/ha/an respectivement. En 1998, les charges sédimentaires des bassins versants RC‑GFS ont été plus importantes que les bassins avec cultures en lignes alors que les volumes de ruissellement et les charges sédimentaires sur ces mêmes bassins ont été plus petits lors d’années avec des précipitations égales ou inférieures à la moyenne. Les bassins avec cultures en lignes et comportant 55 % de pâturages permettent une réduction de l’ordre de 55 % des volumes de ruissellement et de 66 % des charges sédimentaires lorsque comparés aux bassins avec cultures en lignes. Les charges sédimentaires mesurées à l’exutoire des bassins avec cultures en lignes ont été plus élevées pour 90 % des événements que celles issues des bassins avec pâturages ou forestiers. Les résultats de cette étude montrent que des bandes riveraines de 3 à 4 m, le maintien de plus de 55 % du territoire sous forme de pâturages/CRP pour des bassins avec cultures en lignes et la présence de bandes riveraines permettent de réduire de façon significative les volumes de ruissellement et les charges sédimentaires des bassins versants avec cultures en lignes.