While the effect of residents is small, the usage of other sectors is, ultimately, in service of residents. People raise cattle in response to or anticipation of demand. Those cattle use more water than if we raised chickens or wheat for seitan. I consider it unlikely that a top down campaign to ration beef, in service of water usage, would succeed without a change in residential culture.
I am more apt to agree with Hank Green [0] that success in major social restructuring requires involvement at the individual level, too, because this encourages secondary behaviors that reinforce the restructuring. People who are voluntarily quitting hamburgers and steaks are more apt to write to their representatives or donate to NGOs that do in support of this issue, initially and to check in later on that promises are kept.
[0] https://www.youtube.com/watch?v=bvAznN_MPWQ
As another example, Alec, who publishes youtube videos as _Technology Connections_, recently published a video about using his house as a thermal battery [1] so he can offset his energy use to night time, rather than running his AC at peak hours. He suggests that utilities involve residents to widen this strategy, in favor of brownouts or other centralized tools for shedding load in extreme circumstances. A policy solution that did not burden individuals with brownouts, ex by overprovisioning generation, would fall back on their shoulders in the form of higher utility rates. I allege the same would be the case for adverse climate change or overallocated water usage.
[1] https://www.youtube.com/watch?v=0f9GpMWdvWI
