Shower water recycling.
In Australia we have a big water shortage problem with lots of great ideas about desalination and grey-water recycling flying around, but the only way to collect and re-use shower water is to put buckets in the shower with you or start replumbing. Theres got to be a better plan.
I'm thinking along the lines of a 10cm high X 90cm X 90cm plastic storage box that fits in the shower recess with a nice teak top to stand on and an inbuilt hand top. Bilge pump to empty the water as required. Overflow would still go down the usual drain and I estimate it could hold up to 80 litres or 10 buckets worth. Grey water can be used on plants and shouldn't be stored so the plan would require it to be self draining too.