Mumbai residents need not buy reverse osmosis (RO) water purifiers as a study by the Union Consumer Affairs Ministry has found samples of tap water collected from the financial capital compliant with the Indian standards for drinking water. However, other metro cities of Delhi, Kolkata and Chennai failed in almost 10 out of 11 quality parameters tested by the Bureau of Indian Standards (BIS) which is under the aegis of the Consumer Affairs Ministry. Similarly, samples drawn from 17 other state capitals were not as per the prescribed specifications for drinking water.