Do we know how much water India actually has?  Yes  No  Can’t say

As India faces a scary water crisis, the question that floats in mind is how much water do we really have? Turns out we may not have the answer.

Methodologies used to calculate the availability of water are not adequate and need to be revised, experts told Down To Earth (DTE).

There are different estimates for the availability of surface water, including basins, sub-basins, watersheds, rivers, water bodies, urban and rural population extents, dams, barrages, canals and command boundaries. But these are not assimilated to determine a comprehensive figure.

The Central Water Commission (CWC) gives out figures for glacial lakes/water bodies in the Himalayan region, state-wise details of dams, reservoir levels, and water quality.

However, all these figures are in isolation. Moreover, the record of the available quantity in each of these sources belongs to different periods.

For example, the last updated data for glacial lakes/water bodies is from 2011, while the data for dams includes estimates from different states as and when provided by them.

A paper published in June 2016 in the Current Science journal had noted that the available information and data collected so far by different field organisations, scientific groups and engineers was poor for planning, development and management of the vast water resources in India.

“So far, data collection, processing, storage and dissemination have not received adequate attention and are not well organised,” said Rakesh Kumar, scientist at the National Institute of Hydrology, and one of the authors of the paper.

“An accurate assessment of available surface and groundwater resources, considering the human-made changes, is needed for planning, design and operation of the water resources projects as well as for watershed management. There should be a periodic reassessment of the surface and groundwater potential on a scientific basis,” he added.

Others agree.

“We only have limited data based on conservative estimates,” S Arya, professor at IIT Roorkee’s Department of Hydrology, said.

“Most methodologies are working on estimates on how much water we receive and how it goes into different sources. So when it comes to water resource assessment, the computation is done, say every ten years on how much rainfall goes in different sources. So this is basically water auditing. But basins have a different nature, catchments have different characteristics and one single methodology cannot work,” he noted.

It is very difficult to ascertain how much water is available from which source and how much can be tapped with the current methodologies, said Dipankar Saha, former additional director, Central Pollution Control Board (CPCB).

He added that the need of the hour was to get water quantity data at the block or district level and ascertain present and projected requirement according to population and how much water extraction and what types of activities should be allowed with that available quantity.

“Accordingly, a development plan can be made area-wise. All the areas cannot be developed uniformly in the country. The need of the hour for the newly formed Jal Shakti ministry is to bring all available data on a single platform,” said Saha.

According to Arya, modelling at a basin-level is the way forward.  

“Whatever data is available is not homogenous across basins. Especially for Himalayan rivers coming from the mountains where climate is diversified, the data is not representative of the area as it is in plains,” he said.

Hence, said Arya, data should be studied at a basin scale where different varied characteristics of the catchments can be studied. Following this, tools, which are applicable in the different catchments can be selected.

“We require at least 30-40 years of data before we could conclude anything. The CWC has now started focusing on this. In a period 10-15 years, we will be having enough data to reach a point where we can say we have this much water in India,” he said.

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