The aesthetic quality of the water is something immediately apparent to the consumer and is responsible for the vast majority of complaints. It is sometimes listed in terms of organoleptic parameters which relate to the organs of sense. The parameters listed in the E.C. directive include colour, turbidity, odour and taste. Each is considered separately.
COLOUR – water can have a yellowish hue in some instances. This is usually present in water taken from upland catchment areas and is due to breakdown products of plants e.g. humus.
TURBIDITY – turbidity can be caused by three general types of material.
Suspended solids may be present due to disturbances of solid materials in water mains. They will usually settle on standing.
Colloidial materials are present as very fine solids and will not settle out on standing.
Microbial activity can give rise to turbidity but is unusual in freshly chlorinated water.
Examples of substances which can cause turbidity are organic compounds, iron, manganese, aluminium, zinc, bacterial growths, and air.
ODOUR – this can be due to the presence of organic substances although many consumers have noted the characteristic odour due to chlorination.
Hydrogen sulphide has a strong odour but only a very low level is allowed in water to prevent problems. Hydrogen sulphide can form in deaerated water due to the breakdown of sulphate by sulphate reducing bacteria. This occurs in stagnant water and must be controlled immediately.
TASTE – taste problems are responsible for most complaints about water quality.
Substances which can be responsible for taste problems include chloride, sulphate, sodium, copper, iron, zinc, magnesium, calcium, chlorophenols (antiseptic taste) and chlorine. In fact chlorination is a problem for Water Authorities because the water should be dosed at such a level to achieve a satisfactory bacterial kill, but not impart a significant taste. The level of chlorination therefore has to be carefully monitored.
Natural processes can also impart a taste to water. This is usually recognizable as a musty, earthy taste.