What precisely is this fascinating substance water?
Webster defines it briefly as: "The liquid which descends from the clouds in rain, and which forms rivers, lakes, seas, etc. Pure ordinary water (H20) consists of hydrogen (11.1888 percent) by weight and oxygen (88.812 percent). It has a slightly blue color and is very slightly compressible. At its maximum density at 39.2 °F or 4 °C, it is the standard for the specific gravities of solids and liquids. Its specific heat is the basis for the calorie and the B.T.U. units of heat. It freezes at 32 °F or 0 °C"
Note the term "pure water" in this definition. Though we talk a great deal about "pure water," the phrase is more of a designation than an actuality. Actually, "pure water" (H20) occurs so rarely, that for all intents and purposes, it is a non-existent liquid.
Even the term "pure water" is somewhat ambiguous. It has different connotations to individuals in various fields. The bacteriologist, for example, is apt to regard "pure water" as a sterile liquid, that is, one with no living bacteria in it. The chemist, on the other hand, might well classify water as "pure" when it possesses no mineral, gaseous or organic impurities. It is obvious that "pure water" as described in this paragraph is likely to be found only in laboratories ... and even there only under ideal conditions.
The United States Environmental Protection Agency (EPA) provides practical standards for water in terms of its suitability for drinking (or potability) in the Primary Drinking Water Regulations and for aesthetic considerations in the Secondary Drinking Water Regulations.
In its Drinking Water Regulations, the U.S. EPA takes into consideration adequate protection of water against the effects of contamination, both through natural processes and through artificial treatment. The Standards list requirements for bacterial count, physical and chemical characteristics.
It is almost impossible to find a source of water that will meet basic requirements for a public water supply without requiring some form of treatment. In general, the requirements for a public water supply may be considered as follows:
- That it shall contain no disease-producing organisms.
- That it be colorless and clear.
- That it be good-tasting, free from odors and preferably cool.
- That it be non-corrosive.
- That it be free from gases, such as hydrogen sulfide and staining minerals, such as iron and manganese.
- That it be plentiful and low in cost.
While the presence of coliform bacteria and toxic chemical content in a water supply would cause a water to be classified as unsafe to drink, other factors such as taste, odor, color and mineral content have a certain aesthetic effect - which can cause a water to be rejected as a usable supply. A potable, or safe water, is not necessarily usable or useful for many purposes. For this reason it may require treatment of another sort to render it useful to the needs of the home or industry ... or for use by the space age scientist, for example. In any event, no snap judgement should be the basis for determining whether or not a certain water can meet requirements for a certain use.
There are tremendous variations in the quality of water from area to area. Review of the maps at the end of the article gives some indication of the variations. These, however, are only broad general indications of the differences. Even within a specified area significant differences may be noted.
In some cases there are variations in the quality of water in a given area, even on a day to day basis. Why do such variations occur?
The answer can be traced to the fact that water is a solvent. Water is aptly described as "the universal solvent." Scientists generally agree that it is one of the best solvents available.
As a result of its solvent action, water dissolves at least a portion of everything it touches. It dissolves metals, rocks, waste matter, gases, dust and numerous other foreign substances and may contain appreciable amounts of these dissolved materials.
The dissolved mineral content of water ranges from 20 to 80 parts per million (milligrams per liter) in areas where there are only slightly soluble granite formations. From this low level it increases quite noticeably depending on area conditions.
The dissolved solids content of the oceans is in the 35,000 ppm (mg/l) range. It is estimated that there are enough dissolved solids in the oceans to cover all the earth's land surfaces to a depth of 112 feet. Each year inland waterways carry billions of tons more of dissolved solids into the oceans.
In any area, the dissolved solids content of a water supply may vary sharply depending on whether the water is drawn from a deep well, a lake, a river or a pond.