The National Compilation of Dynamic Ground Water Resources is a biennial report published by the Central Ground Water Board, Ministry of Jal Shakti, Government of India. It details the state of ground water from the state and union territory, to the district and blocks of districts (Taluks) level for all districts.

The report calculates the total annual groundwater availability based on the rainfall received and other sources. It also calculates the total groundwater extracted each year. The stage of groundwater extraction is computed based on this as the percentage of the total annual groundwater availability that is extracted annually.

This percentage if classified into the following stages:

• “Safe” where less than 70% of the annual available groundwater is extracted
• “Semi-critical” where between 70 to 90% of the annual available groundwater is extracted
• “Critical” where the extraction is between 90-100% of the available groundwater
• “Over-exploited” when the annual extraction exceeds the annual availability.

Imagine ground water as a bank account from which you can withdraw money to spend. Every year you receive an income that is deposited into the account. Initially, when the population in an area is less, there are more green spaces, more aquifers in the form of tanks and lakes and more water seeping into the ground, more money is deposited into the account. Borewells that extract this water spend money from the account, but as borewells and wells were shallower the amount extracted was smaller and the amount withdrawn each year was less than what was deposited. This adds to the balance in the account every year. In ground water terms it is called fossil water.

As the population in the area grows, as green spaces are lost due to concretisation, as lakes and tanks are encroached upon, the annual income into the account starts reducing. In parallel, as more and deeper borewells are drilled to sate the increasing population, the amount that is withdrawn from the account starts growing rapidly. A tipping point is soon reached when the amount withdrawn every year exceeds the amount being deposited. When this happens you start withdrawing the earlier balance, the fossil water. Eventually, like in an overdrawn bank account, the balance goes to zero and there is no water left to extract. This is called a Day Zero situation.

Stage of groundwater extraction in major cities

According to the national compilation of ground water resources – 2022, two of India’s large metros – Bengaluru and Chennai are in over-exploited stage, while three others – Delhi, Hyderabad and Kolkata are in the Critical stage, bordering on 100%. Pune and Ahmedabad are in semi-critical state. No information on Mumbai was available in the report.

In terms of usage, different cities use groundwater for different purposes. While most of the groundwater extracted in Chennai, Delhi and Hyderabad is for domestic purposes, in Pune, Ahmedabad and Bengaluru irrigation (agriculture) dominates the usage. The usage for agriculture in Pune is high enough to make a separate chart without it!

High usage for irrigation is a factor of the presence of villages within a district. In the case of Chennai, Delhi and Hyderabad, the city corporation area covers almost the entire district, while in the case of Bengaluru Urban, Ahmedabad and Pune districts, the district covers an area much larger than the city council limits where there are still villages which depend on agriculture for their livelihood. Despite the presence of industries in most cities, the usage is higher than domestic only in Bengaluru and Ahmedabad.

Looking only at domestic usage, Delhi ranks the highest followed by Chennai, Pune and Hyderabad. Despite popular perception Bengaluru ranks well behind the other metros in terms of domestic usage. This is mainly because of the Cauvery water supply to most areas of Bengaluru.

The groundwater situation in Bengaluru, Chennai and Delhi over the years

To understand the groundwater situation in three major metros where the usage is either over-exploited or close to that, we looked at the extraction over the years for Bengaluru, Chennai and Delhi. The data for Hyderabad is incomplete in some of the years and had to be excluded because of that.

The compilation report is available only for the following years – 2004, 2009, 2011, 2013, 2017, 2020 and 2022. The x-axis in charts below also reflect that and should not be seen as a timeline with equal intervals.

Looking at the stage of extraction, Delhi seems to have gradually moved to critical stage from over-exploitation over the years. Chennai’s groundwater exploitation percentage seems to be declining gradually and if the trend holds they can go below 100% at some point in the future. Bengaluru’s situation however looks grim. But given how the usage is mainly towards irrigation and industries, the chances of it declining soon are remote.

Looking at the total groundwater extracted over the years, we see a different picture. All three metros show a rapidly increasing trend, at least since 2020.

The situation is the same when looked at the domestic and industrial demand for ground water. In fact, Bengaluru’s demand is almost the same as Chennai in 2022. While Chennai’s usage of this is predominantly domestic, in Bengaluru it is industrial.

The stage of groundwater exploitation has remained constant despite this because the amount of water available each year has also increased proportionally.

The extractable ground water amount is dependent on two sources – rainfall and what is put down as “other sources” – seepage from water supply, tanks and lakes, which can be fed with stormwater or sewage, or rivers and streams like in Delhi.

The recharge from rainfall has seen an uptick from the 2020 report onward. This has been possible because of excess rainfall in 2020 and 2018; the 2022 and 2020 reports use rainfall from 2020 and 2018 respectively to compute rainfall related recharge.

The ground water recharged each year is calculated by using the total area under consideration, the rainfall over the year in mm and a 30% infiltration factor. For instance if 1000mm rainfall fell over Bengaluru in a year, only 300mm of it is estimated to have infiltrated to recharge the ground water levels.

Recharge from other sources has remained mostly constant over the years for Bengaluru and Chennai. Delhi sees some variation year on year, but it has remained constant between the 2020 and 2022 reports.

The road ahead

What this suggests is that while usage has been going up, the stage of extraction hasn’t gone up alarmingly only because the years considered received excess rainfall – the money deposited in those years was also higher than average.

Usage of groundwater proceeds without heed to amount of rainfall received in any year. As we grapple with poor rainfall over this year and the next because of the El-Nino, the next report would probably show a higher percentage rate of extraction.

While reduction in water used for domestic purposes might not be possible, in places like Bengaluru, Pune and Ahmedabad, efforts must be made to move agriculture away from water-intensive crops. Industries should be weaned away from groundwater towards using treated wastewater. For this, we first need efficient and large-scale wastewater treatment infrastructure. Treated wastewater can also be used for domestic purposes like washing cars, clothes, gardening etc.

On the other side, we need to make concerted efforts to save more of the rain that falls on our cities. Mandatory rain-water harvesting and conserving our waterbodies can help recharge the groundwater tables making sure we have more in the bank every year to draw from.

A conversation in Ernest Hemingway’s “The Sun Also Rises” goes like this:
Bill: “How did you go bankrupt?”
Mike: “Two ways. Gradually, then suddenly”.

This could well be the path of our cities to day-zero if we don’t act soon.