Entirely automate the process like a washing machine
- Start showering in a mixture of water and a measured amount (great saving here) of suitable detergent. e.g. Pantene
- Recycle round the soapy water before the drain for a few minutes
- Sound buzzer and wash down with clean water
- Squirt out measured amount of conditioner
- Cut all water for time for human to agitate and leave conditioner to work
- Wash down with clean hot water
- Sound buzzer then squirt out powerful shower cleaner detergent
- Wash down with cold water
- Squirt out some strong lemony fragrance
Could engineer in some heat recovery from drained water.
Also if human remains standing in the shower at step 7, then they will eventually learn not to....