I think we've been working quite hard on that problem. Most of the detergents I use today (in the UK) are now cold water detergents, that don't need warm water

I think we've been working quite hard on that problem. Most of the detergents I use today (in the UK) are now cold water detergents, that don't need warm water for every day use. Modern front-loading washing machines use about 50 litres (10 gallons) for a full load - about a fifth of old top-loaders. I seem to recall some research into using ultrasound to clean fabrics, but I'm not sure where we are on that.