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Source to tap: How water reaches homes in Delhi

The recent face-off between a Union Minister and the Delhi government has raised a crucial question: How clean is Delhi’s water? The Indian Express traces its route from two rivers to your tap, and discovers the checks and balances along the way

Written by Shivam Patel | New Delhi |
Updated: November 25, 2019 7:13:22 am
Delhi water quality, water quality Delhi, Delhi water quality test, AAP Delhi water, Delhi Jal Board, Delhi water quality test, indian express news, Delhi city news, Delhi news A recent report by the Bureau of Indian Standards (BIS), released by Union Minister Ram Vilas Paswan, found the capital’s drinking water quality as the worst among 21 cities surveyed, including Mumbai, Hyderabad and Kolkata.

A challenge has been thrown to the Aam Aadmi Party-led Delhi government by the Centre just before the national capital goes to polls early next year, this time over the city’s water quality. A recent report by the Bureau of Indian Standards (BIS), released by Union Minister Ram Vilas Paswan, found the capital’s drinking water quality as the worst among 21 cities surveyed, including Mumbai, Hyderabad and Kolkata. Soon after, debates raged in the Parliament, press conferences and online, with terms such as “politically motivated,” “poison water” and “scaremongering” thrown into the mix. A re-test is about to happen over the next few weeks of 3,000 water samples from across the city — a far higher number than the 11 samples assessed by the BIS — to determine the “truth”.

Against this backdrop, The Indian Express followed the journey of Delhi’s water, from the source to the tap, to understand and assess how it reaches our homes.

The process

“An experienced eye can easily tell the turbidity in water by just looking at it,” said a central laboratory officer at the Delhi Jal Board’s Haiderpur water treatment plant (WTP), who did not wish to be named. Turbidity is a measure of suspended particles in water — a higher turbidity makes water more cloudy.

“There have been times, around monsoon, when it reached as high as 6,000 and the water then looks red because a lot of mud gets mixed in it. But we can still bring it down to 1, as is the quality standard,” the officer said.

Delhi’s two main surface water sources are the Yamuna and Ganga which, officials said, account for around 90% of the water supply. The remaining is covered by ground water. Of the 10 treatment plants run by the DJB, the Sonia Vihar and Bhagirathi WTPs in East Delhi get raw water from the Ganga through pipelines stretching from Muradnagar in Uttar Pradesh, while eight others rely on the Yamuna and ground water supply. The process starts after raw water enters the treatment plant.

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.

Kejriwal, too, has maintained that water quality of any city cannot be determined based on 11 samples, as done by the BIS. He said that as per WHO guidelines, one sample should be taken for every 10,000 people, based on which 2,000 samples should have been assessed from Delhi. Complaints of bad water quality are received from less than 125 areas in the city at present, the CM said, as against over 2,300 when the AAP came to power in 2015. The joint BIS-DJB survey would test five samples from homes in every municipal ward — apart from UGRs, treatment plants and raw water sources — and the results would be put out in public domain.

The AAP has questioned the process adopted by the BIS for its recent water quality report. DJB vice-chairman and AAP MLA Dinesh Mohaniya has alleged that the standards body may not have tested all 11 samples — he claimed one was taken from an address that did not exist and the occupant of another said no sample was collected from his place.

He also claimed that one sample was taken from the house of a member of Paswan’s Lok Janshakti Party (LJP) and that at a fourth address, the occupant said an LJP worker had collected the water sample and not the BIS. The DJB also tested samples from 9 out of 11 addresses covered by the BIS, of which eight were found fit for drinking, Mohaniya said.

Paswan, on the other hand, has challenged the CM to remove ROs (reverse osmosis purifiers) from Delhi government offices: “If tap water in Delhi is pure, then Kejriwal should announce the removal of ROs from government offices and start providing tap water in official meetings.”


Sampling is done by the DJB every day during water supply hours, for which houses and UGRs are picked randomly. At a primary UGR in Rohini, a DJB employee drew in water from a tap to test whether it has “residual chlorine”. To find out, a solution is put in a glass tube and water is added in it. The colour of the water added to the tube turned yellow right away, meaning it had chlorine. Samplers also check the exact amount of chlorine present in the water using a separate method.

The problem of contamination arises, Srivastava said, when consumers start using electrical pumps to draw in water during odd hours, when water is not supplied by the DJB and the pipelines are empty. “If a lot of people are using pumps at the same time, it creates a vacuum in the pipe; if there’s a breakage somewhere, dirty water will seep through it… If someone has done unauthorised connection, and it’s not done properly, the Jal Board line gets tampered and that will contaminate further connections in that line as well,” he said.

“When (improper connections) are made by a large number of people in a colony, then the water pipe becomes ruptured everywhere. You then have to replace the whole pipe,” Srivastava added.

The problem also arises if a water pipeline has completed its lifetime and needs replacing but is still being used, or if any construction activity on the roads damage the pipes. On an average, the DJB changes around 250 km of its water network every year, officials said.

There’s also the problem of ammonia, which is found in potable water supply if sewage mixes with it. Large amounts of it also enter the WTPs when industrial effluents are released by Haryana into a drain which gets mixed with raw Yamuna water, a DJB official said. This affects the Chandrawal, Wazirabad and Okhla WTPs.

Production here has to either be stopped completely or affected water has to be diluted to treatable levels, with raw Yamuna water diverted through pipelines. All three WTPs are being fitted with advanced technologies to treat high levels of ammonia.

With a re-assessment of the city’s water quality about to take place, the DJB is positive it will meet all standards. Mohaniya also said water supplied by the department is fit for drinking without any additional purification required. The report of the re-test is expected to be released in a month.

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