There are no reduction schemes on water rates for disabled people or benefit recipients offered by any of the water companies in the UK that I am aware of, but there are schemes set up by some authoritiess that do help out with exessive bills ie. alternative or easier methods of repayment ... best to check with your local water authority as each area is different.
If you're on a unmetered water supply, it may be worth considering installing a water meter depending on your usage, if you're a low volume user and you anticipate there may be any savings to be made.