Additional home connection on existing water line?

Can someone tell me if it is possible to connect an additional house connection (with an extra valve) to an existing water connection? My wife's brother is our direct neighbor (the property was recently divided between my wife and her brother) and would allow this. This would save us the cost of breaking up the street. However, the water supplier claims that for legal reasons, every house needs its own water connection to the supply line. But there is nothing about this in the statutes. Does anyone know the current legal situation regarding this?