1. A separation and reclamation system for producing a concentrate solution having a relatively constant solute concentration from a feed solution having a variable solute concentration comprising: solvent separation means having an inlet for introducing feed solution into said solvent separation means and an outlet for removing concentrate solution from said solvent separating means, said solvent separating means further including a semipermeable membrane for preferentially passing the solvent of the solution in said solvent separation means; a recycle connected with said outlet for recycling a portion of said concentrate solution through said solvent separation means; a concentrate valve connected with said outlet for removing a portion of said concentrate solution from said system and for varying the rate at which the concentrate solution is removed from said system, said recycle and said concentrate valve further functioning to maintain sufficient flow through said outlet and over said semipermeable membrane so as to limit precipitation of solids on said membrane; and a valve control means for controlling said concentrate valve including a concentration sensing means for detecting the relative solute concentration of the solution in said outlet between said solvent separation means and said concentrate valve, means for opening said concentrate valve when the solute concentration in said outlet is greater than a preselected value, the extent to which said valve is opened being proportional to the extent to which the solute concentration in said outlet is greater than said preselected value, and for closing said concentrate valve when the solute concentration in said outlet is less than said preselected value.