In an effort to reconcile the problems posed by a growing population and shrinking water supplies, city councilors are contemplating a plan that would retrofit existing buildings with water-saving toilets. The Public Utilities Committee has recommended that the full council adopt a plan whereby builders would retrofit toilets to earn credits toward new building permits. To earn a new building permit, builders would have to retrofit eight to 12 toilets in existing structures. The plan ties together two different water-conservation visions: reining in the water-hungry construction industry, and reducing water demand by improving efficiency in plumbing.