I am building a house that will be supplied by a water cistern (well-fed or trucked in) that will gravity feed into the basement. In order to supply domestic water (2 people, but 4 baths) that will include a multi-head shower and supply water for landscaping, I'm thinking I need a pump/tank that provides up to 18 gpm @ 40 psi continuously (at the same time, not 18 gpm OR 40 psi)? Does someone have a recommendation for a pump/tank system that can provide this kind of performance? Should I be looking for different specs? Thanks very much.