When I was a child, we used to share bathwater - I had the bathwater after dsis, and mum and dad shared a second lot later on - mum first, then dad. Admittedly, we did have baths twice a week, not once a fortnight, but still.
The reasoning was that we had a very old immersion heater, with no thermostat, and it cost too much to heat up the water, so we had to share.
I didn't mind too much when I was a child, because I got to stay up later than dsis as she was younger, so that seemed like a fair reward for having the used bathwater, but when we were teenagers, and had the same bedtime, I started to resent the fact that dsis always got the clean, hot water, and I didn't, and that I had to clean up the bath and the bathroom after my bath, and she didn't - so I asked mum if dsis and I could take turns to have first go in the bath - and she said NO!!
That's one of the things that cemented my view that she preferred my sister to me - she always made me feel second best. Though in recent years I have also wondered whether she refused partly because, if she acknowledged that it was unfair to me, she'd also have had to acknowledge that it was unfair to my dad, and she didn't want to have to have the used bathwater and clean up the bathroom!!
Stupidly, this still makes me sad.