How you know your water is safe to drink

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How you know your water is safe to drink
Water quality refers to the chemical, physical, biological, and radiological characteristics of water and is all about measuring the condition of water against the purpose the water is going to be used for. It is most frequently used by reference to a set of standards against which compliance can be assessed, the most used of course being the safety of the water destined for human contact and drinking water.

Water Quality Standards

In the setting of thse standards, the agencies make political and technical/scientific decisions, on a whole range of subjects. Different uses raise different concerns and therefore different standards are considered. The source of the water is often a natural water body and as these vary in response to environmental conditions, much attention is given to the way they are tested and standards these are to be tested against.


Categories of Water

The parameters that water quality must meet is determined by the intended use, most work being focused on water that is treated for human consumption, industrial use, or in the environment.

Human consumption

This is the most stringently tested group, as the contaminants that may be in untreated water include microorganisms such as viruses, protozoa and bacteria; inorganic contaminants such as salts and metals; organic chemical contaminants from industrial processes; pesticides and herbicides; and radioactive contaminants, any of which are potentially hazardous.


Industrial and domestic use

Dissolved minerals could also affect the suitability of water for a range of industrial and domestic purposes. The most familiar of these is probably the presence of ions of calcium and magnesium which interfere with the cleaning action of soap, and can form hard sulfate and soft carbonate deposits in water heaters and boilers. Hard water may be softened to remove these ions. This softening process often however substitutes sodium cations. It is said by some however that hard water is preferable to soft water for human consumption. The softening process however does decrease nutrition but may increase cleaning effectiveness

Environmental water quality

Environmental water quality, also called ambient water quality, relates to water in bodies such as lakes, rivers, and oceans. The water quality standards for surface waters can vary significantly due to different environmental conditions, ecosystems, and of course where the intended use is for human consumption, as the latter areas often are protected by extra bye laws and rules.

Toxic substances and high populations of certain microorganisms can even present a health hazard for non-drinking purposes such as irrigation, boating and industrial uses. These conditions may also affect wildlife, which use the water for drinking and / or as a habitat. Modern water quality laws generally specify protection of the water bodies in fisheries and for recreational use and have the standards that must be met.



Sample collection


Automated sampling stations are often used to ensure water quality standards, the more complex measurements being made under laboratory conditions. Such testing requires water samples to be collected, preserved, transported to the lab and this itself introduces two significant problems. The first problem is the extent to which the sample may be representative of the water source being tested, as many water sources vary with time and or location. The second problem occurs as the sample is removed from the water source and begins to establish chemical equilibrium with its new surroundings - the sample container. Sample containers must thus be made of materials with minimal reactivity with substances to be measured and pre-cleaning of sample containers is important.


Chemical analysis


The simplest methods of chemical analysis are those measuring chemical elements. Elemental analysis for dissolved oxygen, as an example, would indicate a concentration of 890,000 milligrams per litre (mg/L) of water sample because water is made of oxygen. The method selected to measure dissolved oxygen should differentiate between diatomic oxygen and oxygen combined with other elements.

Water analysis for heavy metals must consider soil particles suspended in the water sample, as these suspended soil particles may contain measurable amounts of metal. This is because even though the particles are not dissolved in the water, they may be consumed by people drinking the water.

Filtration of soil particles from the water sample before acid addition, however, may cause loss of dissolved metals onto the filter. As can be seen the complexities of differentiating similar organic molecules are even more challenging.

Making these complex measurements can thus be expensive and the right equipment is needed in all cases.