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Drinking water should be clear, bright, colourless, adequately aerated and with no discernible taste, odour, suspended matter or turbidity. It should be pleasant to drink and free from harmful organisms and should not contain excessive amounts of certain chemical substances.

Guidelines for impurities...

Drinking water should be clear, bright, colourless, adequately aerated and with no discernible taste, odour, suspended matter or turbidity. It should be pleasant to drink and free from harmful organisms and should not contain excessive amounts of certain chemical substances.

Guidelines for impurities.

Test Maximum desirable level

Colour 50 units
Turbidity 25 units
Odour unobjectionable
Taste unobjectionable

pH 6.5 - 9.2
Total solids 1500 mg/L
Calcium 200 mg/L
Magnesium 150 mg/L
Iron 1 mg/L
Chloride 600 mg/l
Zinc 15 mg/L
Copper 1.5 mg/L
Cadmium 0.01 mg/L
Sulphate 400 mg/L
Nitrate 10 mg/L

E. coli In any year, 90% of samples should not
contain more than 2 per 100 ml

Drinking water should be aerated because water containing dissolved oxygen provides a more pleasant taste. Freshly distilled water tastes 'flat'.

The colour of naturally occurring water is mainly due to dissolved organic compounds derived from rotting vegetation.

A bath full of water with a colour rating of 10 units has a noticeable colour. If the water is 50 units you cannot see the bottom of the bath. Some of the opaqueness of water may be due to suspended solid particles (turbidity).

Irrigation - salt tolerances

Measuring water quality

The concentrations of each of the common ions in solution

Total dissolved solids (TDS) a measure of the total concentration of all solids dissolved in the water. It is measured by filtering off suspended particles then evaporating the water and weighing the residue.

Hardness - due to the dissolved calcium and magnesium salts

Turbidity - a measure of how opaque the water is and depends upon the quantity of suspended clay particles in the water

Acidity - usually expressed as a value on the pH scale

Biological oxygen demand ( BOD ) a measure of the amount of oxygen used by biological materials in the water. A high BOD indicates a high level of contamination by microorganisms.

Nitrogen to phosphorous ratio (N/P) a measure of the relative concentrations of nitrogen-containing and phosphorous-containing nutrients in the water.