Hello, I am a solicitor with over 15 years experience. I will try to help you with this.
You need to find out if your neighbour has an easement for the supply of water through your property. An easement is a right of use for a specific purpose over land owned by another. Your solicitor should have told you about all the easements affecting your property, alternatively if you look at your title register at the land registry this will list the easements affecting your property. This can be done on line at http://www.uklrs.co.uk/