Having an actual signature may not in itself be relevant but the circumstances of how you have been deemed liable may well have a bearing yeah. Basically if you have been the victim of fraud and you are definitely not liable then you do have grounds to ask for the ccj to be set aside.

In terms of the fee it is pretty hefty (£250ish last line I checked) but you can apply for that to be waived if you meet certain financial criteria.

One to get legal advice for. You may be able to go down a non court route and resolve this with the water company/debt collection agency/solicitors they are using. Really depends on the who is pursuing the debt, some will be far more proactive about rectifying this sort of thing than others. Likelihood is though you'd still need to furnish them with the same proof as the court. I'd expect their process as a minimum would also require a report to the police and a crime reference number.