Water quality
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To most people not professionally involved in water quality issues, water is either drinkable (technically potable) or contains potentially harmful or toxic substances. However, the vast majority of surface water on the planet is neither potable nor toxic. This remains true even if we eliminate from consideration the more than 97% of the earth's water found in the oceans (sea water)—too salty to drink. Another general perception of water quality is that of a simple property that tells whether water is polluted or not. In fact, water quality is a very complex subject, in part because water is a complex medium intrinsically tied to the ecology of the entire planet.
Interest by individuals and volunteer groups in making local water quality observations is high, and an understanding of the basic chemistry of many water quality parameters is an essential first step to making good measurements. Most citizens harbor great concern over the purity of their drinking water, but there is far more to water quality than water treatment for human consumption. In point of fact, purification of drinking water is really a different, although obviously related, subject altogether. Many people in the world live where community water purification is simply not a reality. For these people, water quality, even for drinking purposes, relates directly to the local stream, lake, or groundwater. Thus, at its heart, water quality is about preserving uses. Not only use of water as a consumable product, but all other uses such as wildlife habitat, irrigation, swimming, fishing, rafting, and boating—any or all of which can be adversely impacted by water quality degradation. Of course, industrial uses are also important, and industries are always interested in the quality and quantity of water available to them.
Statements to the effect that "uses must be preserved" are included within water quality regulations for the reason that they provide for broad interpretation of water quality results, while preserving the ultimate goal of the regulations. Technical measures of water quality—that is, the values obtained when making water quality measurements—are always subject to interpretation from multiple perspectives. Is it reasonable to expect a river to be pristine in a landscape that no longer is? If a river has always carried sediment, is it polluted even if the cause is not man induced? Can water quality be maintained when water quantity can not? The questions that arise from consideration of water quality relative to human uses of the water become more complex when consideration must be given to conditions required to sustain aquatic biota. Yet inherent in the concept of preserving uses is a mandate that waterways must be much more than conduits for a fluid we might want to drink, fill our swimming pool with, or carry our wastes out of town.
Measurement of water quality
The complexity of water quality as a subject is reflected in the many types of measurements of water quality. These measurements include (from simple and basic to more complex):
- Conductivity (also see salinity)
- Dissolved Oxygen (DO)
- pH
- Color and odor
- Turbidity
- Total suspended solids (TSS)
- Chemical oxygen demand (COD)
- Biochemical oxygen demand (BOD)
- Fecal coliform bacteria (e.g. Escherichia coli)
- Nutrients (fertilizers)
- Dissolved metals
- Dissolved organics
The simple measurements (towards the top in the listing above) are those that can be made with an instrument, in most cases in the field (in situ). The more complex or difficult measurements are those that come from analytical methods, typically requiring a water sample to be collected, preserved, and later analyzed in a laboratory setting. These latter measurements can be expensive and it is always important to understand in advance the reason(s) for making any particular measurement. Also, because the number of substances that could be present in a water sample runs to the millions, it is not possible to reasonably establish what all might be in a particular sample without a very large budget. If the logic of this fact is difficult to grasp, the inefficiency should be obvious: to satisfy such a request, a laboratory would have to charge for determining the more that 99% of possibilities that are NOT present in the sample to discover the minutely less than 1% that are.
See also
External link
- World Health Organization water quality guidelines (http://www.who.int/water_sanitation_health/dwq/gdwq3/en/)
- U.S. National Water Quality Monitoring Council (NWQMC) [1] (http://water.usgs.gov/wicp/acwi/monitoring/)
- European Environment Agency [2] (http://reports.eea.eu.int/92-9167-023-5/en/tab_content_RLR)
- USGS [3] (http://water.usgs.gov/nawqa)
- U.S. Environmental Protection Agency [4] (http://www.epa.gov/owow/monitoring)
- U.S. National Agricultural Library [5] (http://www.nal.usda.gov/wqic)nl:Waterkwaliteit