Not a drop to drink

AT a recent seminar on water management in Karachi, most participants complained of the poor quality of drinking water in their respective localities.

According to newspaper reports, high levels of fluoride have been found in wells in the Thar area, while the Jinnah Postgraduate Medical Centre (JPMC) in Karachi is getting contaminated water. There are also reports of the presence of arsenic in the wells of Arbab Allah Bux village near Tando Allahyar.

This write-up attempts to put water quality problems in their true perspective in order to inform the reader about the source of water contamination and measures that are appropriate to specific water quality problems.

The Karachi Water & Sewerage Board claims to provide potable water that has been purified at water treatment plants. Citizens, on the other hand, complain that they get contaminated water. The appropriate way is to have a third party analyse the water quality once a month and make public its findings.

No matter what input has gone into the designing of a water treatment plant, it will not yield safe drinking water unless it is operated according to the designed considerations. For example, the typical permissible filtration rate for rapid-sand filters (the type of water treatment plants used in Karachi) is three gallons per minute per square foot. If this rate is exceeded, the filter units are unable to give the desired treatment, and the final water quality will be poor. Similarly, the use of chemicals in low quantities or of inferior quality will affect the efficiency of the plant.

Because of inadequate pressure, water cannot reach the underground tanks of homes. People have to use suction pumps to draw water. The widespread use of suction pumps creates negative pressure in the pipes, allowing sewage to be drawn in through weak joints. The sensible approach, in this case, would be to provide drinking water 24 hours a day, seven days a week, with adequate pressure. This would prevent the use of suction pumps and there would be no water contamination.

Escherichia coli are organisms normally used as indicator organisms, indicating fecal contamination. Since the identification of E.coli is complex and time-consuming, the thermotolerant coliform count is often used. Thermotolerant coliform organisms can ferment lactose at 44oC and comprise primarily E.coli and a few strains of other organisms (Enterobacter, Klebsiella and Citrobacter).

Coliform organisms are less resistant to disinfection. Enteroviruses and the cysts of some parasites are more resistant. Therefore, the absence of coliforms in disinfected water does not necessarily indicate the absence of enteroviruses or the cysts of Cryptosporidium, Giardia, amoebae and other parasites.

While over 80 per cent of the people in Karachi boil water, many still suffer from health problems (fatigue, neurological problems and carcinogenic complications). The reason is simple. Boiling inactivates bacterial contaminants only. It does not remove potential health-threatening contaminants like DDT, lead, nitrates, chromium, trihalomethanes (THMs), etc. Also, it is debatable, whether boiling fully inactivates enteroviruses and cysts.

Since there is no provision of tertiary or advanced water treatment in Karachi’s plants, all health-threatening contaminants in raw water escape treatment and end up in finished water. Source protection is not practised by water service providers. Because of the heavy use of agrochemicals in catchment areas, chemicals like DDT, phosphates and nitrates flow down to the raw water source. Industrial wastewater is not treated. Heavy metals, therefore, also find their way to the raw water source.

THMs are formed when chlorine reacts with humic substances in raw water. THMs include chloroform and bromoform. Chloroform is carcinogenic. Water service providers need to switch disinfectants from chlorine to chlorine dioxide or ozone to prevent the formation of THMs. Drinking water in Karachi has never been tested for THMs.

Arsenic contamination in groundwater is due to the presence of arsenic ores in the underground strata. Two possible suggestions can be made. One, arsenic-laden wells should be discarded. Surface water or wells not affected by arsenic should be used. In case of surface water, full-scale water treatment would be required.

Second, if there is no other choice, filters kits may be used. However, proper tests must be carried out to ensure that these are able to remove arsenic and to note the time period during which they are effective. Filter kits, depending on the water quantity use and the levels of arsenic in raw water, typically lose their efficiency after two months of operation. The World Health Organisation has given the maximum permissible limit of arsenic in drinking water as 0.01 milligrams per litre (mg/l).

Fluoride is unique in the sense that drinking water must have a fluoride level of 0.5 mg/l to prevent dental decay. On the other hand, if the level of fluoride is greater than 1.5 mg/l, it will cause dental fluorosis (yellowish or brownish striations or mottling of the enamel) and crippling skeletal fluorosis. For mitigation, the first option would be to find alternate water sources. If this is not possible then defluoridation techniques (activated alumina, contact precipitation, bone charcoal) are available, which can be used. Activated alumina can concurrently remove other anions such as arsenate.

Three decades of experience in water engineering have shown me that when it comes to water quality problems, water service providers adopt an evasive attitude and resort to a blame-game. Also, technical expertise in the water department is of poor calibre.

Despite the fact that it is known that the catchment areas feeding the water source have changed drastically over the years in terms of their characteristics and the type of water received, water service providers are content with the rapid-sand water treatment system. They know quite well that conventional water treatment plants are ineffective in removing heavy metals, pesticides and agrochemicals.

Water treatment plants in Karachi and Hyderabad must have tertiary or advanced water treatment units in addition to the rapid-sand filtration system so that toxic contaminants, which are not removed by conventional water treatment plants, can be eliminated. Likewise, disinfection byproducts (THMs) should also removed by adopting the appropriate disinfection system.
Courtesy Daily Dawn Lahore / By By F.H. Mughal