Many different contaminants can make water unsafe to drink. They include organisms such as bacteria, viruses and parasites and inorganic matter, such as chemicals.

In 1974, the U.S. Congress passed the Safe Drinking Water Act to establish legislation protecting the nation’s public water supply. The guidelines of this legislation apply to the more than 160,000 public water systems in the United States.

Various treatment methods help make drinking water safe for consumption. For example, water that has been chlorinated to minimum standards will protect people who drink it against various contaminants. However, no method of treatment can completely guarantee that all contaminants will be eliminated. Aging infrastructure and natural disasters, such as floods, can allow contaminants to leach into water supplies.

In addition, some people rely on private wells for drinking water. Because these people are responsible for the safety of their water supply, experts urge them to have their wells tested annually for the presence of nitrates and coliform bacteria.

In some areas, the tap water may not be chlorinated, or hygiene and sanitation may be especially poor. This can allow contaminants to seep into the water, causing health problems in those who consume the water. When possible, people who cannot access properly treated tap water are urged to choose canned or bottled water and other safe beverages.