Environmental Health Ch. 9 Water Quality

Water Scarcity

". . . a country faces water scarcity when its annual supply of renewable freshwater is less than 1,000 cubic meters per person." "Such countries can expect to experience chronic and widespread shortages of water that hinder their development."

Water Stress

"A country faces water stress when its annual supply of renewable freshwater is between 1,000 and 1,700 cubic meters per person." "Such countries can expect to experience temporary or limited water shortages."

Aquifer

"A layer or section of earth or rock that contains freshwater, known as groundwater (any water that is stored naturally underground or that flows through rock or soil, supplying springs and wells)."

Wetlands

"Wetlands include swamps, bogs, marshes, mires, lagoons and floodplains."

Reservoirs

Artificial lakes, produced by constructing physical barriers across flowing rivers, which allow the water to pool and be used for various purposes. The volume of water stored in reservoirs worldwide is estimated at 4,286 km3...."

Renewable Water

"Freshwater that is continuously replenished by the hydrological cycle for withdrawal within reasonable time limits, such as water in rivers, lakes, or reservoirs that fill from precipitation or from runoff."

Glaciers and Icecaps

"Glaciers and icecaps cover about 10% of the world's landmass." "These are concentrated in Greenland and Antarctica and contain ~70% of the world's freshwater."

Freshwater Lakes

"Most freshwater lakes are located at high altitudes, with nearly 50% of the world's lakes in Canada alone." "Many lakes, especially those in arid regions, become salty through evaporation, which concentrates the inflowing salts." Examples of major salt lakes are the Caspian Sea, Dead Sea, and Great Salt Lake.

Hydrological (Water) Cycle

"The natural cycle by which water evaporates from oceans and other water bodies, accumulates as water vapor in clouds, and returns to oceans and other water bodies as precipitation

Runoff

"Water originating as precipitation on land that then runs off the land into rivers, streams, and lakes, eventually reaching the oceans, inland seas, or aquifers, unless it evaporates first."

Surface Water

"all water on the surface (e.g., lakes, rivers, reservoirs, ponds, and oceans) as distinguished from subsurface or ground water."

Groundwater Under the Direct Influence of Surface Water

"any water beneath the surface of the ground with substantial occurrence of insects or other macroorganisms, algae, or large-diameter pathogens (e.g., Giardia intestinalis or Cryptosporidium), or substantial and relatively rapid shifts in water characteristics

Finished Water

"the water (e.g., drinking water) delivered to the distribution system after treatment, if any."

Source Water

"untreated water (i.e., raw water) used to produce drinking water."

Groundwater

"water that is contained in the interconnected pores in an aquifer."

Water Disinfection Byproducts (DBPs)

Chemicals used to disinfect water include chlorine, chloramines, chlorine dioxide, and ozone. These chemicals are associated with by-products of chlorination called DBPs. Chlorine is associated with trihalomethanes (THMs), which are among the most common and widely measured DBPs

The Four Stages of Water Treatment in Most Plants

Coagulation-removes suspended material Sedimentation-causes heavy particles to settle to bottom of tanks for collection Filtration-removes smaller particles Disinfection-kills bacteria or microorganisms

Waterborne Diseases

Conditions that are "transmitted through the ingestion of contaminated water and water acts as the passive carrier of the infectious agent." Examples are: Cryptosporidiosis Cholera Certain viruses

Water Withdrawal

Removal of freshwater for human use from any natural source or reservoir, such as a lake, river, or aquifer. If not consumed, the water may return to the environment and can be used again."

Chemicals in the Water Supply

Some chemicals that have been reported to cause adverse health effects: Aluminum Arsenic Disinfection by-products Fluoride Lead Pesticides Radon

Fluoridation of Water

Some communities in the United States add fluoride to public drinking water in order to prevent tooth decay. Field trials conducted in the 1940s demonstrated a 50%-70% reduction in the prevalence of dental caries

Regions That Are Facing Water Scarcity and Water Stress

Two sections of the world that currently have severe water shortages also are experiencing some of the highest population growth rates in the world. Africa (sub-Saharan and North) Near East

Nonrenewable Water

Water in aquifers and other natural reservoirs that . . . [is] not recharged by the hydrological cycle or . . . [is] recharged so slowly that significant withdrawal for human use causes depletion. Fossil aquifers are in this category

Treatment of Water for Residential Consumption

Water supplied to the public in the U.S. undergoes treatment in order to meet quality standards set by the EPA for safe levels of chemical contaminants and waterborne microorganisms.