Water is often disinfected before it enters the distribution system to ensure that dangerous microbes are killed. Chlorine, chloramines, or chlorine dioxide most often are used because they are very effective disinfectants, and residual concentrations can be maintained to guard against biological contamination in the water distribution system. Ozone is a powerful disinfectant, but it is not effective in controlling biological contaminants in the distribution pipes.
Organic contaminants, color, and taste- and odor-causing compounds can stick to the surface of granular or powdered activated carbon (GAC or PAC). GAC is generally more effective than PAC in removing these contaminants. Adsorption is not commonly used in public water supplies.
Ion exchange processes are used to remove inorganic constituents if they cannot be removed adequately by filtration or sedimentation. Ion exchange can be used to treat hard water. It can also be used to remove arsenic, chromium, excess fluoride, nitrates radium, and uranium.
Flocculation refers to water treatment processes that combine small particles into larger particles, which settle out of the water as sediment. Alum and iron salts or synthetic organic polymers (alone, or in combination with metal salts) are generally used to promote coagulation. Settling or sedimentation is simply a gravity process that removes flocculated particles from the water.
In a typical community water supply system, water is transported under pressure through a distribution network of buried pipes. Smaller pipes, called house service lines, are attached to the main water lines to bring water from the distribution network to you house. In many community water supply systems, water pressure is provided by pumping water up into storage tanks that store water at higher elevations than the houses they serve. The force of gravity then “pushes” the water into your home when you open your tap. Houses on a private supply usually get their water from a private well. A pump brings the water out of the ground and into a small tan within the home, where to water is stored under pressure.
Drinking water comes from surface water and ground water. Large-scale water supply systems tend to rely on surface water resources, and smaller water systems tend to use ground water. Including the approximately 23 million Americans who use ground water as a private drinking water source, slightly more than half of the population receives its drinking water from ground water sources.
Surface water includes river, lakes, and reservoirs. Ground water is pumped from wells that are drilled into aquifers. Aquifers are geologic formations that contain water. The quantity of water in an aquifer and the water produced by a well depend on the nature of the rock, sand, or soil in the aquifer where the well withdraws water. Drinking water wells may be shallow (50 feet or less) or deep (more than 1,000 feet). Your water utility or your public works department can tell you the source of your public drinking water supply.
On average, our society uses almost 100 gallons of drinking water per person per day. Traditionally, water use rates are described in units of gallons per capita per day (gpcd), gallons used by one person in one day. Of the “drinking water” supplied by public water systems, only a small portion is actually used for drinking. As residential water consumers, we use most water for other purposes, such as bathing, toilet flushing, cooking, cleaning, and lawn watering.
The amount of water we use in our homes varies during the day:
Lowest rate of use – 11:30 p.m. to 5:00 a.m. rise/High use – 5:00 a.m. to noon. (Peak hourly use from 7:00 a.m. to 8:00 a.m.)
Moderate use – noon to 5:00 p.m. (Lull around 3:00 p.m.)
Increasing evening use – 5:00 p.m. to 11:00 p.m. (Second minor peak, 6:00 to 8:00 p.m.)
We use tap water for various purposes. A typical family of four on a public water supply uses about 350 gallons per day at home. In contrast, a typical household that gets its water from a private well or cistern uses about 200 gallons for a family of four. In our communities an additional 35 gallons of water are used for public activities such as fire fighting, street washing, and park maintenance.