Drinking water comes from either surface water or ground water or a mixture of both. Ground water is pumped from underground aquifers. A significant majority of water systems in the US have a ground water source. However more people get their drinking water form the surface. Visit our Water Source Table to see where your system gets its water.
Typically, an underground system of pipes delivers drinking water to the homes and businesses. These systems in some cases consist of thousands of miles of pipes and supply millions of people. Drinking water must meet EPA required health standards when it leaves the treatment plant.
Treating the 33+ billion gallons of water delivered everyday requires a wide variety of techniques and methods to remove contaminants. Because of expose to the atmosphere and runoff from rain and melting snow, surface water systems require more treatment than ground water systems
The most commonly used treatments include coagulation (flocculation and sedimentation), filtration, and disinfection. Some water systems also use ion exchange and adsorption.
Coagulation (Flocculation & Sedimentation): Flocculation: This step removes dirt and other particles suspended (not dissolved) in the water. Alum and iron salts or synthetic organic polymers are added to the water to form tiny sticky particles called "floc", that attract the dirt particles. Sedimentation: The flocculated particles then settle naturally out of the water under the influence of gravity.
Filtration: Many water treatment facilities use filtration to remove all particles from the water. Those particles include clays and silts, natural organic matter, precipitates from other treatment processes in the facility, iron and manganese, and microorganisms. Filtration clarifies the water.
Disinfection: Water is often disinfected before it enters the distribution system to ensure that dangerous microbial contaminants are killed. Chlorine, chlorinates, or chlorine dioxides are most often used because they are very effective disinfectants, and residual concentrations can be maintained in the water system.
Improving Safety of Household Drinking Water
A network of government agencies monitor tap water suppliers and enforce drinking water standards to ensure the safety of public water supplies. These agencies include EPA, state departments of health and environment, and local public health departments. The EPA divides the US into 10 regions to facilitate management and reporting. The regions are shown in the figure.
About 96% of the US population is served by a Community Water System (CWS). The EPA monitors and reports safe water violations by the CWS'. The chart below shows the percent of US population served by a CWS with no violations for a given year,
Source: EPA Report on the Environment (ROE): 2010