The water supply pipe is the pipe/s which carry your drinking water from the water main and is usually situated in the highway to your property.
The responsibility for the maintenance of the supply pipe is split between the water undertaker and the property owners. Your water undertaker is responsible for the supply pipe from the connection to the water main up to the point at which the supply pipe leaves the boundary of the public highway.The maintenance responsibility for the remainder of the supply pipe sits with the property owners.
Supply pipes are made of varying materials. In older properties some supply pipes are Lead whilst modern developments will have plastic pipes. If your property has a you can replace this with a new plastic pipe.