Open Cistern RO Reference Design for Philippine Homes: Zero-Waste Drinking Water That a Regular Plumber Can Install

This technical note releases an open reference design for a zero-waste reverse osmosis (RO) drinking-water system adapted to the typical Philippine home, which stores city water in a cistern and supplies the house with a booster pump. A conventional household RO unit sends part of its water down the drain; in this design nothing goes to drain. The rejected concentrate flows back into the cistern, and the purified permeate is stored in a separate drinking-water tank. The system uses only standard parts sold in Philippine hardware and water-refilling supply stores, and every step follows physics a plumber already works with: water flows from high to low pressure, pressure grows with height, and what goes into a tank must come out somewhere. It is a companion to the author's Open Hydro-Infrastructure records for buildings with city pressure, and is released for anyone to build, adapt and improve. Open reference design, not a certified product. Competing interests: the author founded Pure Water Center of SoCal Inc., which sells water purification systems. AI tools (Claude, Anthropic) assisted drafting.