I’ll guess that you are in Australia, zoramil. Australia encouraged citizens to install cisterns to catch rain water run-off and reduced water usage from other sources considerably.
In Los Angeles, the rainwater run-off in 2013, the driest year on record, amounted to an estimated 12 billion gallons, which simply ran into the ocean. That represents about 5% of the total amount of water that was used in L.A. that year. Most of the water usage in L.A. is for watering lawns; so the simple expedient of capturing rainwater run-off and installation of drought-resistant native plants would easily reduce water waste by 10%-15%.
It’s very Ironic I use rain barrel and grey water methods to avoid a city Water Bill, where half the bill maintains Storm run off from Paved surfaces and roof tops. The city owns a reservoir of mountain snow melt. I rains alot here. They are building Bio-cisterns that divert Pavement run off into mini-swills that filter, before returning it to the watershed, with my tax money.