Rainwater harvesting vs water ferrying trains: Which is better?

In Chennai, which is going through one of the worst water crisis, 40 per cent of the piped water supply has been cut as its main source of water — four large reservoirs — have gone dry.

The state government has now allocated Rs 65 crore to bring 10 million litres of water to this parched city by train from Jolarpet, which is 200 kilometres away.

A similar exercise was done in the summer of 2016 in Maharashtra’s Latur district, which had faced a severe drought. Then, a train named Jaldoot made 111 trips to ferry 27.9 million litres to Latur.

Is ferrying water by train the solution? How does this fare against the traditional practise of water harvesting? Could rainwater harvesting replace these trains and how much area would one require to harvest the water carried by the trains to Latur or that they will carry to Chennai?

Let’s look at Latur first and how much rainwater can a hectare of land in Latur harvest?

The average rainfall in Latur is about 800 millimetres a year. One hectare of land is equivalent to 10,000 square metres. So, the total rainfall falling on one hectare of land in Latur in a year is about 8,000 cubic meteres or 8 million litres.

But, we know that not all the rainwater can be harvested. Even if we assume that a conservative 50 per cent of the rainfall can be harvested, about 4 million litres of water can be harvested from a hectare of land in Latur. 

This means that the total water carried in 111 trips of Jaldoot could have been stored in 7 hectares of land in Latur. What is interesting is the fact that Latur’s groundwater recharge is only 10 per cent of its annual rainfall.

Similarly, Chennai gets around 1,400 millimetres of rainfall every year. Using the same calculation, 7 million litres of water can be harvested from one hectare of land in Chennai. For Chennai, only one-and-a-half hectares will be required to replace these water carrying trains.

Carrying water by trains could be an emergency measure. Chennai has a strong tradition of water harvesting. But the problem is that most of these structures are either defunct or poorly maintained. 

Chennai had 19 major lakes covering an area of 1,130 hectares. But these water bodies have been heavily encroached upon reducing their spread to just about 645 hectares. It’s time that we understand the importance of water harvesting.