Only Mumbai meets BIS standards.

If it wasn’t enough that Delhi air is among the world’s most polluted, a new study has now shown that the city’s tap water is the most unsafe among 21 State capitals.

The national capital is at the very bottom of the list, in a ranking based on tap water quality released by the Bureau of Indian Standards (BIS) on Tuesday.

It is among 13 cities, including Kolkata, Chennai, Bengaluru, Jaipur and Lucknow, where all tested samples failed to meet the BIS norms for piped drinking water. In fact, Mumbai is the only city where all samples of tap water met all the tested parameters under the Indian Standard 10500:2012 (specification for drinking water) so far.

Under its flagship Jal Jeevan Mission, the Centre aims to provide safe piped water to all households by 2024, with Prime Minister Narendra Modi promising to spend over ₹3.5 lakh crore on the scheme in his last Independence Day speech.

However, the study, conducted by the BIS for the Union Food and Consumer Affairs Ministry, showed that even in urban areas, which are connected to the piped water network, there is no guarantee that the water is safe for consumption. While it is mandatory for bottled water manufacturers to meet quality standards, the BIS standard is voluntary for the public agencies which supply and distribute piped water.

The Ministry is writing to all State governments to develop a consensus on making the standard mandatory. “Stringent action cannot be taken unless the standard becomes mandatory,” said Minister Ram Vilas Paswan, adding that the objective of this exercise was not to demotivate anyone, but rather to encourage the States to ensure quality potable tap water for all citizens.

The BIS standard involves 48 different parameters. Samples are being tested under 28 parameters so far, leaving out parameters related to radioactive substances and free residual chlorine.

Samples are undergoing physical and organoleptic tests (which identify odour, turbidity and pH levels), as well as chemical tests (which identify toxic substances, pesticide residue and excess metals) and virological, bacteriological and biological tests (which identify harmful organisms and disease carriers).

So far, only Delhi samples have been tested under the final category and have come out clean in that area. The capital’s samples also conformed with parameters for toxic substances and pesticide residue. However, coliform and E.Coli samples were found in all Delhi samples, along with excess metals such as aluminium, manganese, magnesium, ammonia and iron. In addition, all samples were turbid and smelled bad.

The Centre plans to expand the scope of the study, bringing the capitals of the northeastern States and all 100 Smart Cities under the testing regime by January 15, 2020, while all district headquarters are expected to be tested by August 15, 2020.