The three major configurations of reverse osmosis units include spiral wound units, tabular units, and plate and frame units. Tests were conducted on prototype units employing all three configurations, and the membranes were found capable of rejecting 93 to 95% of TDS, 90 to 99% of phosphates, 80 to 90% of ammonia nitrogen, 60 to 70% of nitrate nitrogen, 99 to 100% of particulate matter, 90 to 95% of TOC and greater than 90% of COD. Many of the problems discovered stemmed from the use of prototype units which had not been thoroughly tested and were subjected to repeated mechanical failures. Fouling problems have been partially alleviated by periodically depressurizing the membranes and washing them with enzyme detergents. The success of this method is attributed to protein hydrolysis of the slime layer which coats the membrane. Increasing population has dictated the recycling of a much larger portion of the nation's water. Each time it is re-used, the water picks up greater amounts of dissolved solids. These solids will eventually have to be removed to preserve the potability of drinking water. Also, increasing advances in membrane materials have steadily decreased the cost of reverse osmosis to the point that a reverse osmosis system coupled with primary and sand filtration only has an estimated cost of 35.4 cents/1000 gallons. (WRSIC abstract)