Tap water

Tap water, also known as piped or municipal water, is water supplied through a dispenser valve called a tap.

In many nations, this water is of high enough quality to be considered potable, meaning it is safe for drinking. People rely on this resource for essential daily activities like cooking, washing, and hydration. While indoor plumbing has existed since antiquity, it did not become widely available to the general public until the second half of the 19th century. During the 20th century, tap water became common across many global regions. Today, however, reliable access remains a challenge for people living in poverty, particularly in developing countries. In these areas, the term "piped water" is often used by organizations like WHO and UNICEF to track access to drinking water.

To reach a sink or shower, water travels through a complex distribution system. This system is composed of pipes, fittings, and valves that manage the flow. Within a building, water-using items are categorized as either fixtures or appliances. Fixtures are devices that use water without requiring an additional power source. Most of these items also produce sewage or waste components that must be removed by a separate waste system. To prevent dangerous mixing, systems use an air gap or other methods of backflow prevention. These methods use physical and mechanical principles to ensure clean water does not mix with wastewater.

Engineers use a variety of materials to construct these water networks. Many modern systems use different types of plastic. These include polybutylene (PB) and various forms of polyethylene, such as high-density cross-linked polyethylene (PE-X). Some pipes are made of polypropylene, which can come in different forms like PP-B or PP-R. Other advanced pipes are made in layers, combining materials like aluminum with polyethylene to create a strong structure. Metals are also common in plumbing. These include carbon steel and corrosion-resistant galvanized steel. Copper, specifically deoxidized high phosphorus copper (Cu-DHP), is another frequent choice. To help with water conservation, small plastic flow reducers can be installed to restrict flow by 15% to 50%.

Historically, the materials used for pipes have changed due to new scientific understanding. For many centuries, lead was a preferred material for pipes because it was durable and easy to process. However, lead is toxic to the human body. Using lead pipes caused serious health issues, including high death rates among newborns and miscarriages. In the United States, many lead pipes were installed during the late 1800s. Many of these remain in the Northeast and Midwest today. While the buildup of minerals on the inside of pipes can sometimes slow the release of lead into the water, the material is still considered detrimental. Because of these risks, most modern installations replace lead with copper or plastic.

Maintaining water quality is a massive responsibility handled by governmental agencies. Most regulations focus on the treatment plant rather than the distribution system itself. The goal is to deliver treated, safe water to every service point without any degradation in quality. However, physical, chemical, and biological factors can cause contamination within the pipes. For example, if scientists find fecal indicator bacteria, it suggests the water source may have been contaminated with fecal matter. Another factor is "water age," which refers to the time water spends in the system. Because it can take hours or even days for water to reach a consumer, the size and complexity of the network can affect its stability.

Sometimes, tap water may appear cloudy, which can be confusing to consumers. This cloudiness is usually not caused by mineral impurities, but by air bubbles. This happens because of changes in temperature or pressure. Cold water is able to hold more air than warm water. When the water is heated or the pressure is reduced, the dissolved gas comes out of the solution. This creates tiny bubbles that make the water look milky. This effect is harmless and the cloudiness disappears quickly as the gas is released into the air.

Public perception of tap water often influences whether people choose it or bottled water. Many people prefer bottled water due to concerns about taste, odor, or perceived safety. In the United States, a 1993 cryptosporidiosis outbreak in Milwaukee, Wisconsin, affected more than 400,000 residents. Such large-scale events can decrease public trust in municipal supplies. However, the rise in plastic bottled water consumption creates environmental challenges, such as transportation emissions and the buildup of non-degradable plastics. While the debate over the actual quality difference between bottled and tap water continues, many municipalities encourage tap water use to protect the environment.