I dont know about the rest of the uk,but here in Wales you can apply to the water company for what is called Water Assist. Doesnt matter if you are billed 6mthly,yearly,or on a water meter. If,due to a medical condition,you have to use more water than you normally would do,you can apply for this if in receipt of certain benefits. A Dr needs to sign the application, stating that you, or someone in the household suffers from one of the listed conditions. I was recently awarded water assist. It means I wont pay more than £131 for water or more than £131 for sewerage for the current yearly billing period. Might be worth checking if your water company does a similar scheme.