Recycling of waste water by ion exchange was studied on a bench scale. Secondary municipal effluent, which had undergone lime flocculation, served as a feed for the ion-exchange system. Partial desalination was achieved by allowing part of the feed to bypass the strong acid cation exchanger. The salt concentration was decreased from 15 meq/l (750 ppm as CaCO3) to 7-10 meq/l (350-500 ppm as CaCO3) and the organic matter, from 70-100 mg/l COD (chemical oxygen demand) to about 25 mg/l. The leakage of organic matter in the partial desalination mode was somewhat higher than that found in complete desalination. The resins were found to be highly resistant to an attack of organic matter over a period of one year. Three possible resin arrangements were investigated, and a cost analysis for one of them is presented. Since inexpensive chemicals, such as H2SO4, and Ca(OH)2, can be used for regeneration the system provides an economical method for recycling waste water for industry and agriculture.