Reverse osmosis (ro) water purifiers, the most effective to purify drinking water constitute the largest segment accounting for 42% of the water purifier market revenue in 2011 with 0.4 million units sold across india.one major drawback of ro technology is the huge wastage of water resulting from the purification process. for a typical ro purifier, the ratio of volume of purified water to that of rejected water can vary from 1:4 to 1:10. this ro reject water is highly saline, making it unfit not only for drinking but also for any other practical use. currently available purifiers are not designed to handle the recycling of rejected water. given the increasing water scarcity in india especially in urban areas, there is a massive threat of depletion of water resources at this rate of wastage of water from ro purifiers. we attempt to solve this problem by treating reject water streams from a household to tap water standards. our technology is based on microbial desalination technique, wherein ions present in water are removed through semipermeable membranes. our solution is environmentally friendly with no external electricity usage. we aim to explore the possibility of using microbial desalination to soften ro reject water so that the water can be safely used for household purposes. in the process, we intend to optimize the reactor design and the choice of anolyte and catholyte which makes the setup more energy efficient, cost-effective and easily adaptable for practical purposes. our setup is made of three compartments: anode chamber with wastewater, cathode chamber with ferricyanide solution both of capacity 32ml and a 15 ml middle chamber where ro reject water is placed. we tested our setup with 50 g/l nacl in deionized water and ro reject water collected from a household in iit madras. the total dissolved salts(tds) in 50 g/l nacl solution in the middle chamber decreased by 53% from 48 g/l to 22 g/l in 72 hours during the treatment. after 72 hours, the anolyte was replaced with fresh mixture of wastewater and acetate medium which resulted in a steeper decrease of tds from 22 to 16 in 20 hours. similarly, the decrease in tds in ro reject water is about 24% from 465 ppm to 336 ppm in 3 hours after which it slightly increased to 350 ppm in 4 hours. the final value of 350 ppm is close to the tds value of tap water (382 ppm) in the same household. from our results, we infer that ion removal from the middle chamber is possible only to an extent after which the ions from anolyte and catholyte might diffuse into the water being. our setup gives higher ion removal rates when the input water is of high tds. as the ions get removed resulting in lowering of tds, the ion removal rates are observed to decrease. we observed that intermittent replacement of anolyte helps in increasing the removal rates at low concentrations of tds. this could be due to the accumulation of removed ions in the anolyte which affects the osmotic pressure and also the growth of microbes in anolyte. we conclude that our solution can treat the ro reject water in less time (3 hours) to a quality of tap water in terms of tds values without any use of electricity. we plan to extend our research towards replacing the ferricyanide solution with air cathode and scaling up our setup to a capacity to treat 1 litre of ro reject water.