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Water quality FAQ Frequently Asked Questions


The question library on water related issues

Which factors determine water quality?

Water quality is determined by the presence and quantity of contaminants, by physical/ chemical factors such as pH and conductivity, by the number of salts present and by the presence of nutrients. Humans largely influence all these factors, as they discharge their waste in water and add all kinds of substances and contaminants to water that are not naturally present.

More information on physical/ chemical properties of water.

What is the difference between salt water and freshwater?

Salt water is water that contains a certain amount of salts. This means that its conductivity is higher and its taste much saltier when one drinks it. Salt water is not suited to be used as drinking water, because salt drains water from human bodies. When humans drink salt water they risk dehydration. If we want to drink seawater, it needs to be desalinated first. Salt water can be found everywhere on the surface of the earth, in the oceans, in rivers and in saltwater ponds. About 71% of the earth is covered with salt water.
Freshwater is water with a dissolved salt concentration of less than 1%. There are two kinds of freshwater reservoirs: standing bodies of freshwater, such as lakes, ponds and inland wetlands and floating bodies of freshwater, such as streams and rivers. These bodies of water cover only a small part of the earth's surface, and their locations are unrelated to climate. Only about 1% of the earth's surface is covered with freshwater, whereas 41% of all known fish species live in this water. Fresh water zones are usually closely connected to land; therefore they are often threatened by a constant input of organic matter, inorganic nutrients and pollutants.

How is water quality assessed?

To determine water quality, certified agencies take samples; small amounts of water in a medium which can be tested in a laboratory. Laboratories test these samples on various factors, and see if they suffice water quality standards.
One of these factors is the number of colonies of coliform bacteria; these are an indicator for drinking or swimming water quality. Another factor is the concentration of certain contaminants and other substances, such as eutrophication agents.

What are water quality certificates?

When water serves a certain purpose, such as swimming water or drinking water, people that use it need to know whether it is safe. A water quality certificate is a piece of paper that is given out by a certified agency for water quality assessment, after the assessments have taken place, when the company is content about the water quality. These certificates show people that water is safe to swim in or to drink. Water quality certificates are given out for example to pool owners. Bottled water sometimes includes a safety brand on the bottles, which shows that a certificate has been given to the supplying company.

More info on water quality standards.



More detailed information on water quality assessment is now available.

For water terminology check out our Water Glossary or go back to water FAQ overview.

Feel free to contact us if you have any other questions.

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