Many residents were seen gathering near water supply tankers with colorful bottles to collect water in Chennai, India, on Saturday, as the four major reservoirs to Chennai have dried up. /VCG Photo

The bed of the Chembarambakkam Lake, one of the largest freshwater reservoirs in Chennai, has gone bone dry. /VCG Photo

Besides the groundwater, the only resource that can support the city currently is the Veeranam Lake and the two desalination plants. /VCG Photo

Regarded as "the worst water crisis in history," it is forecast that 21 cities are likely to run out of groundwater by 2020. /VCG Photo