Increasing water efficiency is likely to result in reduced demand for water, with less water therefore flowing through drains and sewers. Some parties have suggested that this could lead to blockages, drainage problems and homes flooding due to backed up sewerage systems.
In Germany our toilets usually have two buttons, one for the yellow which flushes but with a lower amount of water and the bigger button for the big brown business and maximum water flow.
Depending where you live and depending on drought being a thing in your place of the world, using less water can have unwanted side effects:
backed sewerage systems
not enough water can lead to environmental problems if the sewage isn’t watered down enough for your sewage treatment plant to deal with it or if it goes straight to a river it is worse than with more water (that one is always really bad but definitely extremely worse with less water)
In Germany our toilets usually have two buttons, one for the yellow which flushes but with a lower amount of water and the bigger button for the big brown business and maximum water flow.
Depending where you live and depending on drought being a thing in your place of the world, using less water can have unwanted side effects: