The Safe Drinking Water Act directs the U.S. Environmental Protection Agency (EPA) to establish national drinking-water standards for chemical and biological contaminants in public water supplies. The standards are to be set at concentrations at which no adverse effects on human health occur or are expected to occur from lifetime consumption, allowing a margin of safety; enforceable standards are standards that are feasible to achieve with the use of the best technology available. The standards are to be reviewed periodically to ensure continued protection of public health. Consistent with the requirement for periodic review, EPA asked the National Research Council to evaluate the current drinking-water maximum-contaminant-level goals (MCLGs) and maximum contaminant levels (MCLs) for nitrate and nitrite in public water supplies. The Subcommittee on Nitrate and Nitrite in Drinking Water, convened under National Research Council procedures, reviewed information on the occurrence and toxicity of nitrate and nitrite. The subcommittee evaluated this information in the context of the drinking-water standards for those substances and drew conclusions about the adequacy of the current standards to protect human health.

The nitrate content of drinking water is rising at an alarming rate in several regions of NATO countries and elsewhere in the world. The increase is due to lack of proper sewage treatment, and primarily to excess fertilizer application. Also, eutrophication in several coastal areas is triggered by high nitrate concentrations. The main purpose of this book is to integrate scientific knowledge related to exposure assessment, health consequences and control of nitrate contamination in water. The motivation is related to the magnitude, the possible adverse health effects, and the high cost of control ling nitrate contamination. Future research tasks are defined by an interaction among hydro logists, toxicologists and environmental engineers in an integrated framework for nitrate risk management. The target readership of this book is a mix of university colleagues, practitioners from both the private and public sectors and advanced graduate students working with the hydrological, health science or environmental engineering aspects of nitrate contamination. The main conclusions include: 1. For risk assessment purposes, knowledge and sufficiently accurate models are available to predict nitrate load and its fate in water under changes in land use. 2. Once agricultural exposure controls are implemented, the response times in ground water may be so long as to make controls unrealistic. 3. It is still unknown whether agricultural best management practice is a compromise between nitrate risk reduction and agricultural revenue. 4. The current drinking water guidelines of 10 mg/L NOrN need not be changed.

From the Introduction With regard to nitrate and nitrite, the perceived hazards are to the ecological balance in rivers and lakes, and to human health. Increased nitrate levels in river water lead to increased growth of algae and consequent decrease in the level of biologically available oxygen (BAO). In extreme forms, the algae form unsightly blooms on the water surface, and the BAO level falls below that necessary to support fish and other animal life. At this extreme, there is little dispute that efforts should be made to restore the ecological balance, and this is best achieved by reversing the increase in nitrate concentration that caused the problem. The health hazards are less clear, but include the risk of methaemoglobinaemia in young infants and the possible risk of gastric cancer, particularly in certain high-risk patient groups. These health risks have led to legislation to control the exposure of humans to nitrate from drinking water and as a food additive . . . What can be done about this and how can the problem be solved (if, indeed, there is a problem)? It is normal practice to add nitrate and nitrite to food as a cosmetic and as a preservative. Is this necessary? If so, how much do we need to add? Are there alternatives? What effect does added nitrate have on total nitrate exposure of humans? . . . In this book, we have attempted to answer, or at least to give the background to, some of the questions. . . .

The quality of drinking water is paramount for public health. Despite important improvements in the last decades, access to safe drinking water is not universal. The World Health Organization estimates that almost 10% of the population in the world do not have access to improved drinking water sources. Among other diseases, waterborne infections cause diarrhea, which kills nearly one million people every year, mostly children under 5 years of age. On the other hand, chemical pollution is a concern in high-income countries and an increasing problem in low- and middle-income countries. Exposure to chemicals in drinking water may lead to a range of chronic non-communicable diseases (e.g., cancer, cardiovascular disease), adverse reproductive outcomes, and effects on children’s health (e.g., neurodevelopment), among other health effects. Although drinking water quality is regulated and monitored in many countries, increasing knowledge leads to the need for reviewing standards and guidelines on a nearly permanent basis, both for regulated and newly identified contaminants. Drinking water standards are mostly based on animal toxicity data, and more robust epidemiologic studies with accurate exposure assessment are needed. The current risk assessment paradigm dealing mostly with one-by-one chemicals dismisses the potential synergisms or interactions from exposures to mixtures of contaminants, particularly at the low-exposure range. Thus, evidence is needed on exposure and health effects of mixtures of contaminants in drinking water. Finally, water stress and water quality problems are expected to increase in the coming years due to climate change and increasing water demand by population growth, and new evidence is needed to design appropriate adaptation policies. This Special Issue of International Journal of Environmental Research and Public Health (IJERPH) focuses on the current state of knowledge on the links between drinking water quality and human health.