Even if an apartment uses as less as 5000 litres of water a day it must have a wastewater recycling system which does such a thorough job that the treated wastewater is reused to replace fresh water and not for simply disposing off into the environment in a safe way. It is simply not good enough for treated wastewater to be used for watering lawns, an unnecessary demand. If the water utility can make it mandatory to put in place such a system it would be wise. It would be even wiser for the builder to implement such a system without the law. It would be the wisest that an aware consumer community demands this from the builder so that the pressure comes from all sides.
A dual line in each apartment will ensure use of treated wastewater for non-potable use. Treated wastewater can also be used for recharging the aquifers and suitable laws, protocols and standards need to be developed for this. It would also help if a standard list of approved wastewater treatment technologies is made available for builders to choose from. A third party inspection and certification would also ensure strict adherence to laws and effective implementation.
Other steps to consider is the complete ban on the use of fresh piped water or groundwater for lawns , swimming pools, car wash, sidewalk washing and other such wasteful uses during summer.