The first step is to understand where the problem lies.
The current answers on this page suggest changes in water consumption on the domestic front. What fraction of water consumption do you think occurs in the domestic sector? 80%? 50%? 25%?
There is no need to speculate, we have the data (source).
Attacking the problem at any level other than agricultural would be trying to stop a deluge with a band-aid. They also have the estimates for how the irrigation requirement will play out in the future.
There is nothing we can do to domestic consumption to offset that sort of water requirement. A complete overhaul of agriculture - Perhaps including changing what crops we consume - will be necessary. How do we go about that?