1. Acceptability aspects: Taste, odour and appearance  Water should be free of tastes and odours that would be objectionable to the majority of consumers.  In assessing the quality of drinking-water, consumers rely principally upon their senses.  Microbial, chemical and physical water constituents may affect the appearance, odour or taste of the water, and the consumer will evaluate the quality and acceptability of the water on the basis of these criteria.

2.  Although these substances may have no direct health effects, water that is highly turbid, is highly coloured or has an objectionable taste or odour may be regarded by consumers as unsafe and may be rejected.  Changes in the normal appearance, odour or taste of a drinking- water supply may signal changes in the quality of the raw water source or deficiencies in the treatment process and should be investigated.

3.  The physical parameters affecting acceptability of drinking water are: 1. Taste and odour, 2. Turbidity, 3. Colour, 4. Temperature

4. Taste and odour  Taste and odour originate from:  natural and biological sources or processes  contamination by chemicals  as by-product of water treatment  Taste and odour may develop during storage and distribution.  It is indicative of some form of pollution or malfunction during water treatment or distribution.  The cause should be investigated, particularly if there is substantial change.  An unusual taste or odour might be an indication of the presence of potentially harmful substances.  No health-based guideline value is proposed for taste and odour.

5. Turbidity  Turbidity describes the cloudiness of water caused by suspended particles, chemical precipitates, organic particles and organisms.  Turbidity can be caused by poor source water quality, poor treatment and disturbance of sediments and biofilms or the ingress of dirty water within distribution systems.  Visible turbidity reduces the acceptability of drinking-water. Although most particles that contribute to turbidity have no health significance  Water with turbidity of less than 5 nephelometric turbidity units (NTU) is usually acceptable to consumer.

6. Colour  Drinking-water should ideally have no visible colour.  Colour in drinking-water is usually due to the presence of colored organic matter metals such as iron and manganese, or highly colored industrial wastes.  The source of colour in a drinking-water supply should be investigated, particularly if a substantial change has taken place.  Levels of colour below 15 TCU are often acceptable to consumers.  No health-based guideline value is proposed for colour in drinking- water.

7. Temperature  Cool water is generally more palatable than warm water.  High water temperature enhances the growth of microorganisms and taste, odour, colour and corrosion problem may increase.  No guideline value is recommended.

8. Biologically derived contaminants  There are a number of diverse organisms that often have no public health significance but they produce taste and odour.  They also indicate that water treatment or the maintenance of the distribution system are insufficient.  For example:  Actinomycetes and fungi  Cyanobacteria and algae  Invertebrate animal life  Iron bacteria

9. Chemically derived contaminants Chloride, The standard prescribes for chloride is 200 mg/L. The maximum permissible level is 600 mg/L. Hardness, The taste threshold for the calcium ion is in the range of 100 to 300 mg/L, depending on the associated anion, and the taste threshold of magnesium is probably less than that for calcium. In some instances. Water hardness in excess of 500 mg/L is tolerated by consumers. Ammonia, The threshold odour concentration of ammonia at alkaline pH is approximately 1.5 mg/l, and a taste threshold of 35 mg/l has been proposed for the ammonium cation.

10. pH, An acceptable pH drinking water is between 6.5 and 8.5. PH levels less than 7 may cause severe corrosion of metals in the distribution pipes and elevated levels of certain chemical substances, such as lead may result. At pH levels above 8 there is a progressive decrease in the efficiency of the chlorine disinfection process. Hydrogen sulfide, The taste and odour threshold of hydrogen sulfide in water are estimated to be between 0.05 and 0.1 mg/L. Iron, At levels above 0.3 mg/L, iron stains laundry and plumbing fixtures. There is usually no noticeable taste at iron concentrations below 0.3 mg/L, although turbidity and colour may develop.

11. Sodium, The taste threshold concentration of sodium in water depends on the associated anion and the temperature of the solution about 200 mg/L. Sulphate, The presence of sulphate in drinking water can cause noticeable taste. It is generally considered that taste impairment is minimal at level below 250 mg/L. Total dissolved solids (TDS), Total dissolved solids can have an important effect on the taste of drinking water. The palatability of water with a TDS level of less than 600 mg/L is generally considered to be good. Drinking water becomes increasingly unpalatable at TDS levels greater than 1200 mg/L.

12. Zinc, Zinc imparts an undesirable astringent taste to water at a taste threshold concentration of about 4 mg/L. Water containing zinc at concentrations in excess of 5 mg/L may appear opalescent and develop a greasy film on boiling. Manganese, At level above 0.1 mg/L, manganese in water supplies stains sanitary ware and laundry, and causes an undesirable taste in beverages. Below 0.1 mg/L are usually acceptable to consumers. Dissolved oxygen, Depletion of dissolved oxygen in water supplies can encourage the microbial reduction of nitrate to nitrite and sulfate to sulfide. It can also cause an increase in the concentration of ferrous iron in solution. However, very high levels of dissolved oxygen may exacerbate corrosion of metal pipes.

13. Copper, Staining of sanitary ware and laundry may occur at copper concentrations above 1 mg/L. At levels above 5 mg/L, copper also imparts a colour and an undesirable bitter taste to water. Although copper can give rise to taste, it should be acceptable at the health- based guideline value of 2 mg/L. Aluminum, The presence of aluminum at concentrations in excess of 0.2 mg/L often leads to deposition of aluminum hydroxide floc in distribution system and the exacerbation of discoloration of water by iron.

14. Treatment of taste, odour and appearance problems  In many cases, aesthetic problems will be prevented by optimizing conventional treatment processes such as coagulation, sedimentation and chlorination.  Manganese can be removed by chlorination followed by filtration.  Techniques for removing hydrogen sulfide include aeration, granular activated carbon, filtration and oxidation.  Ammonia can be removed by biological nitrification.  Precipitation softening or cation exchange can reduce hardness.  Other taste- and odour-causing inorganic chemicals are generally not amenable to treatment.