How water reaches Delhi homes - Explained
At Haiderpur, guards are on patrol near a Yamuna canal that supplies water to it to keep “miscreants” away. Inside, the water passes through four processes before it is released to the public. The first is pre-chlorination, which removes impurities at the start. In the next step, polyaluminium chloride and alum is mixed into the water to remove mud and dirt.
“Together they act as a coagulant, meaning they clump the suspended particles in the water so they can be removed in the clariflocculator,” the Haiderpur officer said. In a clariflocculator, which is a large round open tank, clumped particles settle at the bottom and are scraped away as sludge from an outlet below, while clear water is sent further and passed through sand and gravel filters.
An officer, who is part of the treatment operations team in the plant, keeps a register with a neatly drawn table of 13 columns for each parameter that is checked in the water on an hourly basis, before and after treatment, including turbidity, pH level and ammonia. A recent graduate assists the team in testing the water samples in a one-room laboratory.
The plant runs day and night, and staff keep changing every eight hours. The central lab in the plant, equipped with more advanced testing technologies, also checks raw and treated water quality against 30 parameters, with standards set by the BIS. “If any parameter is found to be higher than the standard, we have to make quick decisions. For instance, if ammonia is found to be high, then we either have to dilute raw water or shut production completely,” the officer said.
In the BIS report, all 11 water samples had failed in 19 parameters, including ammonia, turbidity and pH level. Paswan, who had released the report on November 16, had said in Parliament that water supplied by the DJB was not fit for drinking and had challenged Delhi Chief Minister Arvind Kejriwal for a retest. The CM, in turn, called the report false and politically motivated. At present, officials from both DJB and BIS have been appointed for a re-assessment.
Back at the Haiderpur plant, the “political situation” is mentioned occasionally and quickly shrugged off, but a certain pressure is apparent. “I can guarantee that the water which goes out to the public from here is safe for drinking,” the operations officer at the plant said, holding up clear water in his hand after it has passed through the sand and gravel filters.
The final treatment process is post-chlorination. “We add chlorine because… if there is any bacteria, virus or contaminant somewhere in the pipeline, the chlorine reacts with it and kills it after which its own presence is reduced,” said Ankit Srivastava, technical advisor to the DJB.
He said the presence of this “residual chlorine” is tested in about 500 water samples the DJB collects every day from its supply network across the city. If it is not found, then there’s a possibility of contamination somewhere in the pipeline. The samples are also tested against over 25 other parameters.
Waste treatment plants to homes
After water is treated in the plant, it is released into the DJB water pipeline network stretching over 13,000 km. It first reaches a primary underground reservoir (UGR), a reinforced concrete water tank of a large capacity where water is supplied 24×7. However, a DJB officer revealed that while changing pipelines a few years ago, around 200 direct consumer connections were found in between water treatment plants and the primary UGRs — something that is now prohibited. The department now keeps a track of the amount of water received and supplied with 2,200 flow meters installed across its network.
From the primary UGR, water is either supplied directly to colonies based on a fixed time schedule, or is sent to a secondary UGR and in rare cases, a tertiary UGR, which cater to single or a group of colonies. Together, there are nearly 500 UGRs in Delhi. The water pipelines pass in front of houses and it is the responsibility of consumers to apply to the DJB for a connection, officials said. A DJB engineer then assesses the site and recommends how the connection can be made with the help of a DJB licensed plumber.
The water department assesses the quality of water supplied to homes every day, in addition to around 1,500 samples tested at WTPs and of raw water sources. Between January and September 24, 2019, over 1.55 lakh samples were tested by the DJB, of which 2,222, or 1.43%, were found unsatisfactory. In October, more than 16,000 samples were tested, of which 3.98% were unsatisfactory. The DJB states that as per guidelines of the World Health Organisation (WHO) on drinking water quality, 95% of the overall samples assessed in a city have to pass the test. more