After Pallavaram 'water contamination' deaths, TN health dept issues fresh guidelines for chlorination

CHENNAI: In view of the recent deaths in Pallavaram caused by contaminated drinking water and the increasing risks of waterborne diseases from stagnant water and overflowing sewage drains, the Directorate of Public Health and Preventive Medicine has instructed medical officers to strictly ensure regular chlorination of all water sources.

The fresh guidelines issued states that for water chlorination of overhead tanks and ground-level reservoirs and wells, the volume of water in a circular well or tank should be measured and the amount of bleaching powder required for disinfection should be used accordingly. Adequate residual chlorine levels must be monitored consistently to prevent potential outbreaks, it said.

The guidelines also state that overhead tanks must be chlorinated after every filling.

The fresh guidelines have been issued as part of North East Monsoon preparedness.

Also Read: 2 die in ‘drinking water contamination’ at Chennai’s Pallavaram, govt denies

Chlorination is an effective, cost-efficient method to disinfect water, eliminating bacteria, viruses, and parasites that pose health risks. After floods, chlorinating water helps ensure safe drinking water for communities, preventing disease outbreaks and aiding public health recovery.

How to chlorinate

33% bleaching powder should be used in 1,000 litres water with 4 gm of chlorine; 20 ml of 5-6% sodium hypochlorite solution (liquid chlorine) and 0.5 mg of 5-6% chlorine tablet should be used in 1,000 litres of water and 20 litres water, respectively.

1 mg of gaseous chlorine can be used in 1,000 litres of water. For 1MLD (million litres per day) water, 4 kg of 33% bleaching powder, or 20 litres of liquid chlorine, or 1 kg of gaseous chlorine is used.

It is recommended that a minimum residual chlorine concentration of 0.2 mg/L is maintained to the point of delivery to the consumer. For effective disinfection, at least 30 minutes of contact time is recommended, where the residual chlorine concentration is 20.5 ppm and the pH of water is below 8. A residual chlorine concentration between 0.2 and 0.5 mg/L in the distribution network should be targeted.

The mix should be taken in a bucket and made into a paste and water should be added up to three-fourth of the bucket slowly and mixed thoroughly. After lime and sediments settle down, the supernatant chlorine water should be transferred to another bucket and mix the chlorine water in the overhead tank or sump. Liquid chlorine and tablets can be directly added. One hour after the process of chlorination, the water may be used.

The chlorination level should be 3-4 ppm in head works, i.e., the area where wastewater enters a wastewater treatment plant. In overhead tanks or ground level reservoirs and sumps, and tanker lorries it should be 2 ppm. In street fountains, it should be 0.5 to 1 ppm.