The problem is that due to the small volume of water a modern washing machine uses on the wash cycle you probably wouldn't get any of the green heated water into the machine, depending on the length of the supply pipe. So it would have to heat it anyway and would have to move some of your stored hot water from the insulated tank to the pipework to go cold.
Very true. I was thinking of my much missed old Servis 600, one of the first push button digital machines c1982 that had a hot fill and used a respectable amount of water to do the job. I refuse to acknowledge its replacement as a worthy replacement due to the puddle of water it insists on trying to wash clothes in. And everytime it leaves a slight soap powder mark on black things, after it claims to have rinsed them, I show it its own plug to its one big eye at the front, and threaten to cut it off. It will EEEKO the clothes to death for anything up to 2.5 hours if you let it. Even on extra quick it's extra pants.
The ole Servis machine had a hot fill and the washing time could be speeded up even more if you drew off a bit of hot water to the sink just before pressing go. You could easily chop & change its programs and it was done and dusted in about 40mins. And, AND you could even open the door and get your stuff as soon as the drum had stopped spinning. None of this 'Well, I've done them, and I can see you standing there, jumping up and down with your basket all ready, so I taunt you by not unlocking the door for at least 5 minutes. Your mother was a hamster and your father smells of Elderberries'.
Sadly, after 5 outer drum bearings, 2 inner drum bearings, 2 control boards, 2 motors, a handful of pairs of brushes, 3 heaters, 1 inardy drum thingy with a bit of gubbins on it, 2 triacs, several door seals, 1 pump and 22 years of faithful service the Servis 600 was allowed to die.
I don't know if I should admit this on a public forum, but I made it a cake for its 21st birthday. We were such good friends.
Then, in its 8130th day of service (or was it 8131st? I forget) the crack in the diecast drum bearing housing meant that this time, without major major reworkings, that it really was curtains,
and they wouldn't be going in the front.
So after a funeral with full military honours, the body was sent to the home for naughty machines, but its brain and other select highlights were carefully stored away, in a box marked 'Frankenmatic'. Waiting for the day when I have a bit more time to find a suitable donor body. When, it WILL_LIVE_AGAIN.