Microbiology and Immunology

Water quality WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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example, runoff of fertilizers from suburban properties can

infuse watercourses with nitrogen, potassium, and phospho-

rus. All these are desirable nutrients for bacterial growth.

Water purification seeks to convert the polluted water

into water that is acceptable for drinking, for recreation, or for

some other purpose. Techniques such as filtration and expo-

sure to agents or chemicals that will kill the microorganisms in

the water are common means of purification. The use of chlo-

rinationremains the most widely used purification option.

Others approaches are the use of ultraviolet radiation, filters of

extremely small pore size (such that even viruses are

excluded), and the use of a chemical known as ozone.

Depending on the situation and the intended use of the fin-

ished water, combinations of these techniques can be used.

Purification of drinking water aims to remove as many

bacteria as possible, and to completely eliminate those bacte-

ria of intestinal origin. Recreational waters need not be that

pristine. But bacterial numbers need to be below whatever

standard has been deemed permissible for the particular local.

Another microbiological aspect of water pollution that

has become recognized only within the past several years has

been the presence in water of agents used to treat bacteria in

other environments. For example in the household a number

of disinfectant compounds are routinely employed in the

cleaning of household surfaces. In the hospital, the use of

antibioticsto kill bacteria is an everyday occurrence. Such

materials have been detected in water both before and after

municipal wastewater treatment. The health effect of these

compounds is not known at the present time. However, by

analogy with other systems, the low concentration of such

compounds might provide selective pressure for the develop-

ment of resistant bacterial populations.

See alsoChlorination; Waste water treatment; Water quality

WWater qualityATER QUALITY

Water is the universal solvent. Many compounds that can dis-

solve in water are used as food sources by a variety of micro-

biological life forms. These microorganismsare themselves

water-based and their constituent molecules are designed to

function in aqueous environments. Thus, water can widely

support the growth of microorganisms.

Some of this growth is advantageous. For example, the

strains of yeastwhose fermentative abilities make possible the

brewing of beer, the production of wine, and the baking of

bread. In addition, the growth of bacteriain polluted water is

used as a means of decontaminating the water. The bacteria

Sampling polluted water.

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