Water contamination has erupted in Hyderabad with some deaths and many people suffering from stomach disorders. Akram canal besides, supplying water to Badin, also irrigates agricultural lands along the way.

Likewise, the K.B. Feeder which supplies water to Karachi, irrigates lands in Dadu and Thatta districts, as well. Since both these water channels are found contaminated, agriculturists fear adverse effects on their land. Here, the quality of water for irrigation is being discussed.

In the past no consideration was given to the "drainage", resulting in water logging and salinity problems. In Sindh options for environmental management of irrigation and drainage are somewhat limited and, a key aspect is the quality of water. This has not received the attention it should have due to the lack of information.

Over three decades back pollution of surface water bodies was not severe. The river quality was generally good. Accordingly, water from surface water bodies was used for irrigation. The situation has changed now.

Its quality in Sindh has deteriorated. Some canals in Sindh (for example, Akram canal, Phuleli canal, Pinyari canal and the K.B. Feeder) are more polluted, as these receive industrial wastewater in addition to the municipal wastewater.

In the Indus River, in wet season, the impact of pollutants is not felt. However, during low flows (November- February), the salinity impact is felt. Current water quality problems in Hyderabad confirms the contention.

The criteria of water quality varies with the type of use. For example, if water is for drinking, then more emphasis is placed on the bacteriological quality as compared to chemical (this doesn't mean that its chemical quality should be ignored). In bathing, the schisto some cercariae are of concern in areas where schistosomiasis is prevalent.

If water is used for cooling in industrial processes, then importance is on its hardness, corrosiveness and total dissolved solids. In case of irrigation, the emphasis is on quality of chemical and physical characteristics.

Irrigation water quality is also influenced by the application period. Quality criteria for short-term application would be different from the long-term. The short-term standards are more stringent than the long-term. Quality for irrigation should not be considered in isolation but soil properties should also be kept in mind.

Long-term sustainable irrigation demands reasonably good quality along with enough leachate to leach salts from the root zone of crops. This should be supported by efficient drainage to ensure that no water logging exists.

Excessive salts in soil reduce the availability of water to crops. High sodium content lowers the rate at which the applied water enters the soil. High chloride content damages the crop.

Development of irrigation standards should include such interdependent factors as soil properties, plant salt tolerance, climate, and irrigation management. Different crops have different uptake patterns, but all take water from wherever it is most readily available within the root zone.

Each irrigation application leaches the upper root zone and maintains it at a relatively low salinity. Salinity increases with depth and is greatest in the lower part of the root zone.

The average salinity of the soil solution is about three times that of applied water (Petty grove and Asano, 1985). A consulting firm has suggested water quality standards for irrigation.

These are given in Table 1.

Review of the standards, given in Table 1, shows that the standards are overly restrictive. It should be noted that in Sindh, mostly irrigation supply is from one source (typically, a canal). If water quality is classified as "unsuitable" at such relatively lower ranges, a landowner (zamindar) has simply no other option but to keep on using the water.

A better option would be some appropriate measures or restrictions for waters having values of various parameters at higher ranges. Table 2 gives the standards suggested by Wapda.

Pollution of surface water bodies in Sindh is significant and the industrial wastewater is also discharged untreated into water bodies. Since, industrial waste waters contain toxic elements it is necessary to have a guideline value for trace elements in irrigation waters.

The current trend of discharging municipal wastewater in the receiving streams has raised the concern of microbiological quality of water for irrigation. In addition, it is a common practice in rural Sindh for the male population to defecate in fields. This activity is mainly due to the absence of well- ventilated and mosquito-free latrines.

The faecal material is transported to canals due to rains or natural seepage. Conseaquently, it is now considered essential that the irrigation water quality guidelines should have a microbiological aspect, as well.

While, there is a need of quality water for optimum crop production, it is also necessary to control pollution in water bodies. While water treatment is costly, such plants have limitations when it comes to treating difficult waters.

These plants are effective in reducing turbidity and fecal coliforms (depending upon the type of treatment provided), but are not effective in removing most of the trace elements which require more expensive options. Therefore, prevention is better than cure.