I made a transatlantic passage with a young woman who experimented with not washing her long hair, just using talcum powder and brushing it daily. She said that after 10 days of being itchy it settled down and it certainly looked healthy and felt quite normal.
Use salt water wherever posssible. Seawater baths using Joy washing up liquid work well. Use baby wipes. A garden spray with pump and a little fresh water if you feel salt sticky.
Turn off the electric water pump and pump water manually.
Use a presssure cooker.
Related topic Be prepared to collect water off the mainsail. I used a bucket with a U shaped cutaway and a spigot in the base. The first minutes will be slightly salty so separate this if possible.