Hybrid DI systems using CrossCharge technology from Pentair have the benefits of a reverse osmosis (RO) system and those of a water softener without requiring salt.
The CrossCharge technology was developed through a partnership with Dutch firm Voltea and licensed exclusively to Pentair in residential and light commercial applications for point-of-entry products. The new technology uses capacitive electrodes to remove hardness and purify water without employing salt. The core of the system is Voltea’s patented ‘stack’ configuration of electrodes combined with ion-selective membranes. The treatment sequence begins with the purification step, where untreated water flows through the cell where ions are drawn through the membranes and absorbed in the charged electrodes, producing high quality treated water. The electrodes automatically regenerate when the system reverses its polarity. This drives the ions out of the electrodes and flushes them from the stack. The polarity is then reset to normal to start purification again. 
Pentair’s CrossCharge technology is driven by a micro-controller which uses sensors to monitor and manage all system and water quality parameters in real time. The technology assesses the inlet and treated water quality, controls the power supplied to the stack, and adjusts operating cycles and system flows to continuously optimise performance. The controller includes self-diagnostics and auto clean cycles and features a full-colour touch screen user interface.
“Hybrid DI system […] produces 90% less waste water than a conventional whole house reverse osmosis system,” said Alok Maskara, president of Pentair’s Residential Filtration business. “Since it treats water without salt, there is no net increase in discharged total dissolved solids.”