Chronic Illness And Water Advice

I have been diagnosed with Crohn's Disease and I have psoriasis. The last time I saw my consultant, he recommended me contacting Welsh Water to apply for a discount on my monthly bill. I did just that, but was told that because I am not claiming any benefits and I am not on a low income (I work full time), I am not entitled to any discount. I feel this is very unfair as I still use the same amount of water as someone with the same condition as me but who doesn't work. Does anyone know if there is a way around this? Thank you