We have an issue where we are running out of hot water very quickly. I think it is due to the 2 knob (hot/cold) system in our clawfoot tub as well as our shower head.

The question is how can we reduce our water usage and thus not run out of water? we have a 40 gallon hot water heater and have enough for a bath but our shower quickly runs out of water.

Is there a system to change it to a single knob and is there an adaptor to be able to install a low flow showerhead? and if we do that will it cause leaking somewhere else?