Access to safe drinking-water is important as a health and development issue at national, regional and local levels. It has been shown that investments in water supply and sanitation can yield a net economic benefit, as the reductions in adverse health effects and health-care costs outweigh the costs of undertaking the interventions. This edition of the Guidelines further develops concepts, approaches and information introduced in previous editions, including the comprehensive preventive risk management approach for ensuring drinking-water quality that was introduced in the third edition. It considers drinking-water safety, approaches used in deriving the Guidelines, microbial hazards, climate change, chemical contaminants in drinking-water, those key chemicals responsible for large-scale health effects through drinking-water exposure, the important roles of many different stakeholders in ensuring drinking-water safety, and guidance in situations other than traditional community supplies of managed utilities.
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