Sanitation is a basic, as well as a long-standing, public health issue. When early peoples settled in communities and started to cultivate crops and raise animals, sanitation became a primary concern for society. The Book of Leviticus, in the Torah, includes specific guidelines regarding the disposal of wastes, the placement and disinfection of wells, and related issues. Today, as urban areas grow, more pressure has been put on local water supplies, for the quality of the water that is available to a community greatly impacts all aspects of health. Worldwide, 40 percent of the population does not have ready access to clean, safe drinking water, and approximately 60 percent does not have satisfactory facilities for the safe disposal of human waste. Infectious agents in drinking water and food cause the diarrheal deaths of several million children annually.

In the United States, every person uses almost 100 gallons of drinking water per day, though only a small portion of this amount is actually used for drinking. Other uses include toilet flushing, bathing, cooking, cleaning, and lawn watering.

SOURCES OF WATER

Water sources are manifold. Many communities get their water from reservoirs. In 500 B.C.E., the Greeks supplemented local city wells with water supplied from the mountains as far as ten miles away. In later times, the Romans built aqueducts that were many miles long—there are more than two hundred that are still standing in the year 2001. Cities and other communities often provide for their water supply by allocating an open area that is pristine and protected as a watershed. The water is usually of high quality and free from chemical and microbial contamination. These sources are referred to as surface water sources and include lakes, streams, and rivers. Some surface water requires extensive treatment before it can be distributed for human consumption.

In other parts of the country, water is supplied to communities from groundwater sources through deep wells, often many thousands of feet down. Water from these sources is also usually free of chemical and microbial contamination. Groundwater is the main source of drinking water for almost half of the population in the United States. While it is usually free of solids and bacteria, as well as other chemical pollutants, it has often become contaminated by disposal of liquid waste and agricultural runoff. Groundwater is relatively inexpensive, but it is limited in volume and irreplaceable if depleted. By providing protection to the source, either through buffers from the reservoirs or by protecting the well head for the deep wells, water is available without much treatment.

Because of the increasing population and the increased use of water by each individual in the United States, there are less uncontaminated water supplies available. Many sources of water must be treated prior to consumption. Disinfection is an important step in the water treatment process to destroy pathogenic bacteria and other harmful agents. Most water is treated with chlorine, as it is a very effective and economical method of treatment. An important advantage to using chlorine is that it has residual properties and continues to provide germ-killing potential as the water travels from the distribution point to the end users. There are concerns, however, about the formation of disinfection by-products from the reaction of the chlorine with humic substances in the water. These by-products are referred to as trihalomethanes, or THMs. The most common THM is chloroform, which is a carcinogen.

Sanitation includes the appropriate disposal of human and industrial wastes and the protection of the water sources. Waterborne agents are the cause of many diseases in the United States and elsewhere in the world. These diseases may be caused by bacteria, viruses, and protozoans. Bacterial diseases include typhoid, shigellosis, and cholera. Viral agents cause diseases such as include polio and hepatitis. Parasites include the protozoa Entamoeba histolytica and Giardia lambdia, which cause amebiasis and giardiasis, respectively. For the last decade the primary agents in waterborne disease outbreaks in the United States have been the protozoal parasite Giardia, and the bacteria Shigella. Another common agent is Cryptosporidium.

Another example of sanitation as it relates to waterborne diseases globally is schistosomiasis. Schistosomiasis is a chronic debilitating disease with significant morbidity and mortality that affects more than 200 million people worldwide. Sanitation and water supply are important issues in an integrated schistosomiasis control program.

SANITATION AND WATER POLLUTION

Sanitation is directly related to water quality and water pollution. Water quality usually describes the level of certain compounds that could present a health risk. The quality of water is usually defined by guideline values of what is suitable for human consumption and for all usual domestic purposes, including personal hygiene.

In relating sanitation to water pollution, one must examine both point and nonpoint source pollution, as these are the two routes of entry of the pollution into the water supply. Point-source pollutants enter the waterways at well-defined locations, such as a pipe or a sewer outflow. The discharges are usually even and continuous. Industrial factories, sewage treatment plants, and storm sewer outflows are common point sources of pollution. Nonpoint sources enter the water system from broad areas of land. It is estimated that 98 percent of the bacterial contamination and 73 percent of biological oxygen demand are due to nonpoint sources.

WASTEWATER

Water containing human waste is generally referred to as wastewater. In the United States, the disposal of human waste must be handled in a sanitary manner. Usually, this waste is disposed of via a sewer system that uses water as the vehicle for the disposal. Treatment of wastewater is required to prevent pollution of pristine surface waters and groundwater sources. Wastewater treatment consists of physical, chemical, and biological processes. In a typical suburban or urban setting, wastewater from the home enters a domestic or sanitary sewer system. The sanitary sewer is a system of pipes that collects the wastewater, and the waste is transported to a wastewater treatment plant. The water goes through a series of processes that removes the solids from the water. Solids are composted or removed and disposed of via landfill or land application as fertilizer. Sewage consists of more than 99.9 percent water by weight, and the average domestic sewage contains 600 ppm of total solids. The amount of solids present in water has been one of the major water pollution control criteria, due to the relationship of the solids to the oxygen demand.

Water reuse is an important concept that has only recently gained attention and interest in the United States. Water that is reused, commonly known as "gray water," cannot be used on food crops or in any type of domestic use. This water can be used to water landscape and turf. Water reuse will continue to expand as water resources become more and more limited.

Since approximately 1950, a common method of disposal of solids in the United States has been the use of a sanitary landfill. The landfill, which typically is located outside a populated area, is a place where wastes are dumped, compacted, and buried. Special care in siting the landfill must be taken to avoid runoff and leaching of the waste materials into surface water and groundwater. Landfills that are properly designed with the correct engineering and liners can provide adequate protection. In many locations in the United States, these landfills have been sited on marginal land that was unsuitable for industry or agriculture. Many of these sites are sensitive wetland areas that serve as habitat for plants and animal species.

The 1974 Safe Drinking Water Act established a set of primary standards to protect human health. These standards consist of maximum contaminant levels for specific inorganic contaminants, volatile organic chemicals, and radioactive materials, as well as limits for turbidity and coliform organisms. Secondary standards are set for temperature, color, taste, and odor. The Environmental Protection Agency has identified treatment via conventional coagulation, sedimentation, and filtration as effective processes in removing or reducing the levels of contaminants. Societal concerns for the quality of water resources continue as many streams and coastal waters do not meet water quality goals. States report that 40 percent of the waters surveyed are too contaminated for drinking, fishing, and swimming. Since the Clean Water Act was signed in 1972, it is estimated that more than $5 trillion has been spent on water pollution control in the United States.

MARK G. ROBSON

(SEE ALSO: Ambient Water Quality; Biological Oxygen Demand; Chlorination; Clean Water Act; Disinfection By-Products in Drinking Water; Groundwater; Landfills, Sanitary; Municipal Solid Waste; Pollution; Wastewater Treatment; Water Quality; Water Reuse; Water Treatment; Waterborne Diseases)