You mean to say builder has not provided water connection for ground floor flat ?
2) you ought not to have purchased the flat wherein no water connection was provided to you
3) water is an essential service and it is duty of builder to provide you water connection and common water tank for strorage of water
4) issue legal notice to builder to provide you water connection from storage tank
5) if he fails to do so file complaint against builder before RERA and seek orders to direct to provide you water connection and access to water storage tank