Delhi’s water extraction rate better, says report

The Capital extracted 0.36 billion cubic metres (bcm) of groundwater in 2021-2022 but recharged 0.37 bcm during the same year, making it an extraction rate of 98.16%, an improvement from 2020-21 when the extraction rate was 101.4% (more extracted than recharged), the Central Ground Water Board’s (CGWB) latest assessment showed.

The data, released recently, as part of the board’s “Dynamic Groundwater Resources of India, 2022” report, also showed that compared to 2020-21, the number of “safe” tehsils in Delhi has gone up from three to four, while the number of “overexploited” tehsils has dropped from 17 to 15. The state, overall, is still “critical” in terms of groundwater extraction, the report said.

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In 2020-21, 0.32 bcm was recharged during the year, out of which 0.29 bcm was extractable. Approximately 0.29 bcm was extracted, with an overall extraction rate of 101.4% assessed by the CGWB. An extraction rate indicates how much water was recharged in comparison to being extracted. If the rate is over 100%, it indicates that more groundwater was extracted than it was recharged.

At the same time, the report said that in 2021-22, the annual recharge went up to 0.41 bcm, out of which 0.37 was available for annual extraction. Around 0.36 bcm was utilised, meaning the extraction rate was only around 98.16%.

“The increase in the groundwater extraction can be attributed to refinement in the database extraction data, with around 12,000 private tube wells registered with the Delhi Jal Board (DJB) also being incorporated in our estimation. It is also based on refinement in piped water supply, which the DJB has increased in many areas of Delhi. This led to an increase in recharge due to return seepages,” the report said.

Out of the 34 assessment units (tehsils) for 2021-22, 15 units (44.12 %) were categorised as “overexploited”, seven units (20.59 %) were in the “critical” category, eight units (23.53 %) were “semi-critical”, and four (11.76 %) were “safe”. In 2020-21, 17 units were “overexploited”, seven were “critical” range, seven were “semi-critical”, and three were “safe”.

Out of the four safe tehsils, one was in central Delhi, two were in northwest Delhi, and one was part of nazul land (under the government for non-agricultural purposes).

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For groundwater readings, safe zones are those where the ratio of recharge to extraction is 70%, meaning for every 1 litre of groundwater recharge, 0.7 litre is extracted. This can translate to an increase of up to 2 metres each year. In semi-critical zones and critical zones, the ratio is 70-90% and 90-100%, respectively, indicating a limited recharge of 0.5-1 metre each year. In overexploited zones, the ratio is over 100%, meaning the extraction is greater than the recharge and the groundwater table is only going deeper.

A CGWB official when contacted, said a combination of factors has helped Delhi improve. “For 2021-22, an increase in the piped supply network helped improve the groundwater recharge. It is estimated that around 15-17% of the water from piped networks returns to the ground as seepages. The piped supply network has also been included in this assessment. We are also seeing a crackdown on illegal tubewells, with mandatory recharge structures increasing.”