Hello admjh1
No, I don't think you can withold the water charge element of your bill without risking eviction. You have a good argument that the landlord isn't providing you with the whole of the service that you have paid for but I don't believe you can legitimately withold a portion of the rent for the missing service even if your rent bill itemises the water charge separately, because it's all still rent and rent is an entire obligation. It sounds like your committee pays the water company directly out of rent receipts, but that's an arrangement between the committee and the landlord.
It's very unusual to have individual taps, but as that's what you've got, and as previously your rent has included and explicit charge for water, I'd say that you do have a contractural right to water. Like with any other consumer dispute you need to put your complaint in writing to the landlord stating that your tenancy includes the (implied) right to water from your own tap, and if you get no joy follow that up with a final warning that if the landlord won't honour their obligation to supply you will be making a complaint to Trading Standards.
Your landlord can't make you sign a new tenancy agreement. They can however give you notice to terminate your current agreement (at least 12 months notice, and it must terminate on the first or last day of a tenancy year, and you'll need to read your tenancy agreement to see when that is). They can then offer you a new agreement on whatever terms they choose, or they can in fact not offer you a new tenancy at all. That last option is a complete tyrrany because in effect it forces you to sign an agreement at shorter notice that statute allows, but some landlords ar tyrants.
Take heed though: knowing your rights is one thing, successfully sticking up for them is quite another. There's always a chance that a management committee or council clerk will get uppity with you for asserting your rights and making complaints to Trading Standards and such and just decide to evict you, and unless you have a strong site association completely behind you you'll find that very difficult to deal with, so think carefully before you make waves.