After ammonia levels in the Yamuna water at Delhi Jal Board's Nangloi and Haiderpur plants mounted to an all-time high of 3 mg per litre, the DJB wrote to both the Central and Haryana pollution control boards. The Central Pollution Control Board (CPCB) had last year identified four industries in Yamunanagar as the main cause of the problem, but till date the Haryana Pollution Control Board (HPCB) has not been able to control the quality of drinking water reaching Delhi.