It's important to use biodegradable soap & cleaning products when you are re-using your bathwater to water the garden, as normal soap takes a long time to break down from complex chemicals into more useful simple substances that plant life can absorb. So I thought I would write something on biodegrable soap...first of all, look out for vegetable based solid soap like Marseille soap or glycerin soap. Glycerin soap is usually translucent. Marseille soap uses olive oil as a base.
If you prefer to use liquid soap or shower gel, rather than solid soap, you can make your own shower gel by:
 grating solid soap into flakes
 putting these into an old shower gel bottle with some hot water
 Shake the bottle for a few minutes and leave it to stand for a day or too.
This is then ready to use. This is also good for the environment because it stops you buying shower gel bottles which then have to be recycled or just thrown away, ending up in landfill. If you can't be bothered with that, you could use solid soap in the shower, if you have somewhere to put it... you can put in on a string and hang it up above the bath. The best way to do this is to use a screwdriver to grind a hole by hand through the centre of the bar of soap and thread some thick cord through this. Its best to hang the soap high up so its not in the water stream, this way it will last longer.
CHOOSING CLEANING PRODUCTS
As for biodegradeable cleaning products to clean your bath, try using soda crystals or borax. You can buy these sorts of products in cardboard boxes (again less plastic waste) from Clean and Natural by DRI PAK. If you scrub this powder onto the surface of the bath with a bit of water and leave it for a while before washing it off again, it is pretty effortless -on a par with stronger household cleaning products but with less ecological impact. These products are easy and safe to use and odourless. Soda crystals are produced by a relatively simple chemical process which means its more easily broken down, unlike phosphates which are found in more modern cleaning products. for more information on this subject see this page on toxic water by Surfers Against Sewage (SAS)