I think there are some Real Estate Agents who play on the ignorance of tenants who don't understand the law. They are not all like this, but there are some. I find that telling them that I will contact the RTA and get back to them has usually worked well in the past. I have had a couple back right off and tell me not to get my knickers in a knot (I wasn't upset at all, simply stating what I was going to do but I suspect they had a reason to be defensive).

I don't see how they can make you pay it. Also, it is worth finding out if your house is fitted with water saving devices because if it isn't, they can't make you sign a new contract making you responsible for your water usage either. If the water saving devices are fitted, it should greatly reduce the cost of the water bill meaning there is less to pay. It is not your fault if the people that own the house haven't put water saving devices in and the legislation is designed to encourage them to do it.