The “National Compilation of Dynamic Ground Water Resources of India” is an annual report published by the Central Ground Water Board under the Ministry of Jal Shakti, Government of India. The latest report, for 2024 is now out and can be accessed from OpenCity.in here.

Stages of Ground Water Extraction

The groundwater extraction is classified into four categories based on how much is extracted. Each year, based on the rainfall received, the amount of water that got recharged is calculated which gives the “Annual Extractable Groundwater Resource”. The amount of water that was extracted over the year for different purposes – irrigation, domestic or industrial – gives the the “Total Annual Extraction”. The formula “Total Annual Extraction”/”Annual Extractable Groundwater Resource” gives us the “Stage of Groundwater Extraction” which is expressed as a percentage.

Based on this percentage, the report classifies the stages of groundwater extraction into four categories as below.

If this is percentage is 100% it means all the water that was recharged over the year was extracted. The problem is when this percentage exceeds 100% in which case more water was extracted than got recharged. This means that the excess water over the annual recharge came from what is called “Fossil Water”, which is the water that was already there in the groundwater table over the past years when the extraction might not have been as much as now.

Think of it as a bank account where there is an income being received and an expense that goes out. Initially the expenses are low, and income is higher, the account grows and with that what is called savings. However, after a point in time the income stays constant while the expenses start going up steadily. At some point the expenses exceeds the income. At this point, you are dipping into the savings every year. Eventually, a point is reached when the savings are also zero and the expenses can’t be met anymore. In financial terms, it is called bankruptcy. In water terms it is called “Day Zero”, which is when a city runs out of water.

Ground water extraction by states

At the state-level the report finds that most of the states in India are in the safe category. The exceptions are the major farming states of Haryana, Rajasthan and Punjab which are in the overexploited stage. Delhi, with its high reliance on groundwater is also in overexploited stage. Uttar Pradesh and Tamil Nadu are in Semi-critical stage.

At the state level, usage is masked by the inequalities within the states as well as usage within cities and large metros where the water is drawn for domestic purposes. A closer look at our large metros paints a different picture.

Ground water extraction in major metros

Among the major cities, except for Pune and Mumbai, none of the other metros are “Safe”. Ahmedabad is “semi-critical”, but the rest – Bengaluru, Chennai, Hyderabad and Delhi are in overexploited stage, squeezing out as much of the groundwater as they can manage.

In the case of Bengaluru the extraction is at a whopping 186.7% which is probably because the rains in 2023 were well below average because of El Nino.

While the absolute numbers paint a dismal picture, a comparison with the previous year’s usage can give us a clearer idea if things are improving or not.

In this case, except for Bengaluru and Hyderabad, the rest of the cities seem to have improved or have seen only a marginal change in usage. The change is most stark for Bengaluru which went from an already high 150% to 186% of extraction. Hyderabad moved from critical to overexploited in the last one year, joining the other three metros.

While Bengaluru, Hyderabad and Chennai are marked as “overexploited” their states were seen to be either safe or semi-critical. This is usually a factor of other districts not using groundwater as much, either because their areas are larger or that the districts are too poor to use groundwater to grow cash crops.

In the case of Karnataka, the overexploitation is seen mostly around Bengaluru Urban for agriculture in South Interior Karnataka. The economically weaker Kalyana Karnataka region sees much less extraction.

In Tamil Nadu, apart from Chennai, the most extraction was seen in the agricultural districts around the Kaveri basin, which is likely due to the poor rainfall received in 2023. Nagapattinam is interesting in that the groundwater stage is marked as Saline, meaning that the water is not potable.

The southern Karisal (black soil) parts of the state see much less extraction similar to the Kalyana Karnataka region.

Telangana is a study in contrast, where except for Hyderabad, ground water usage is much less in the other districts.

In the case of Delhi, the usage within its much smaller districts isn’t uniform and follows the socio- economic patterns of the districts. Even though the entire region is marked as “Overexploited” a closer look shows that only five of the 12 districts are above 100%.

Where does the water go in the overexploiting cities?

In our highly urbanised metros Bengaluru, Chennai, Hyderabad and Delhi, the ground water usage is expected to go towards domestic usage. However, the report shows some minor variations. In the case of Bengaluru most of the ground water is marked as for irrigation, and the proportion is significant in Delhi too.

The case of Bengaluru is interesting given the large scale shortage of water in the early months of 2024 with private water tankers making merry. Given that a large part of the ground water in Bengaluru arrives through water tankers, it is possible that water extracted from agricultural areas is used to supply large apartment complexes. This would make the extraction agricultural but usage domestic.

This is a gap that is likely being considered by the groundwater authority. While only 11% of the groundwater extracted was considered for domestic usage in 2022 and 2023, that fraction has jumped to 30% in 2024 while the proportion of Irrigation usage has come down correspondingly.

The way ahead

Ground water is an important resource to help a city meet its water needs, but it requires that it be used sustainably. Many cities across the world are dependent heavily on groundwater and have had their trysts with Day Zero where they run out of water. While Cape Town in South Africa and Sao Paulo in Brazil made the news in recent years, this list also includes Bengaluru, Jakarta and rich cities like London and Tokyo.

Usage of ground water is not connected to the actual rainfall that is received. On a poor rainfall year like 2023, the extraction percentage shows a much higher value as the denominator is smaller. While this is a small consolation, the report assumes that around 30% of rainfall received is conserved and goes towards recharging groundwater aquifers, which is very optimistic. Many estimates expect this to be around 5% given the increasing concretisation of our cities. This means that the extraction percentage could be even higher.

What we need are solutions were we can use our ground water more sustainably. There are solutions in the form of better recharging of ground water resources through extensive rainwater harvesting. Rainwater harvesting also helps use rain water to meet a large part of the needs of a city. Treated waste water can be used especially for industrial and construction purposes, relieving the load on ground water.

While solutions exist, strong policy is needed to ensure sustainable usage of ground water resources, or we might be starting at Day Zero sooner rather than later.