Is there a water kettle or dispenser that can keep the water lukewarm?
The easiest tool I can think of is a thermos - fill it with water at or slightly above your desired temperature and enjoy your supply for a few hours.

On a larger scale, a tankless heater can give you a basically unlimited supply of water, but is almost certainly overkill.

Please be careful with all devices that keep water at around 100F / 37C, this lukewarm water will encourage the growth of microorganisms, aka a biofilm. This is also an issue with all water dispensers / coolers, which should also be cleaned regularly.