I don't have a specific study reference, but some keywords to look for are low-volume shower head retrofits (and new ones), low-volume toilets in use, usage of on-demand inline water heaters instead of tanks, "garden" farmers using drip irrigation or hydroponics, shift to all-shower (no bathtub) usage. Other behavioural things to look for are the number of "baths/showers" taken, and why.