Abstract: A source liquid including a solvent with a dissolved impurity flows into a reservoir. The source liquid or a concentration of the source liquid is pumped from the reservoir through a pressure exchanger into an upstream side of a liquid-separation module. The module includes a membrane that at least partially purified solvent as filtrate to a permeate side of the liquid-separation module while diverting the impurity in a feed retentate on the upstream side of the liquid-separation module. The substantially pure water is extracted from the permeate side of the liquid-separation module, while the feed retentate is passed from the upstream side of the liquid-separation module through the pressure exchanger, where pressure from the feed retentate is transferred to the feed from the reservoir. The feed retentate is then passed from the pressure exchanger to the reservoir and recirculated as a component of the feed via the above steps.