Water Education - Water and Health

Oxygen in Drinking Water Supply

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Oxygen adds to the taste of water. For this reason, a small amount of it is desirable in drinking water. We are all familiar with the "flat" taste which water often possesses after it has been standing in an open container for some time. The taste can be improved simply by shaking the water in a partially filled bottle. This reintroduced oxygen into the water will give it a more appealing taste.

Despite this desirable feature, dissolved oxygen can be a source of serious trouble in a household water supply - it causes corrosion. In cold water, oxygen normally has a little corrosive effect. In contrast, when the water is heated, the oxygen can cause serious corrosion problems.

A number of chemicals are used in industry to remove oxygen from a water supply. Sodium sulfite (Na2S03) is probably the most widely used for this purpose. It reacts with oxygen at high temperatures to form sodium sulfate (Na2S04), in this way reducing the oxygen. There are a number of chemicals that react similarly with oxygen to effect its removal. The degree of success varies. For household purposes treatment is normally limited to the use of polyphosphates to coat the insides of water lines to protect the metal from contact with oxygen.

Henry's Law. The English chemist, William Henry, formulated a law regarding the effect of pressure on a gas. The law states: The weight of a gas that dissolves in any given liquid is directly proportional to the pressure, providing the temperature remains constant. If one gram of oxygen, for example, dissolves in 100 cubic centimeters of water at atmospheric pressure, two grams of oxygen will dissolve under twice the normal atmospheric pressure, providing there has been no change in temperature.

How do humans interfere with the amount of dissolved oxygen?

  1. Human intervention comes in the form of dams, human waste, fertilizer, and agricultural waste.
  2. Dams slow the flow of water which reduces the amount of aeration and increases the temperature.
  3. Human waste carries a large amount of oxygen consuming bacteria. Raw sewage can spill into the waterway and introduce bacteria into the water that will use up large amounts of dissolved oxygen.
  4. Fertilizers create algae blooms and plants cannot live without sunlight. The reduction of plants causes less dissolved oxygen.

These are all things we can try our best to prevent. Let us respect our environment and give it the care that it needs. One by one we can all make a difference, stay positive!

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