Using 5% of your water on something entirely optional seems like a good place to start cutting.
If targeting California homeowners of all the loud, politically active groups of people to achieve an absolute best case scenario of 5% gains is a good way to start, you’re not going to finish.
Sure, but it will help some. There is no silver bullet for solving our water resource problems. It is going to take a massive patchwork of partial solutions to even approach something resembling a solution. Balking at small changes is a sure way to ensure that we never make progress. In the post-script of the 2016 update to the book, Cadillac Desert, Mark Reisner makes the point that during the time L.A. County's population increased 40%, it's water usage remained constant due to it's water conservation efforts. That is huge not just for water resources but also CA's greenhouse gas targets. It takes a tremendous amount of energy to pump water from the Delta down to southern California and over the mountain ranges that encircle Los Angels.