Researchers have invented a material called ARUBA — Arsenic Removal Using Bottom Ash — that effectively and affordably removes arsenic from Bangladesh groundwater. Through analysis of studies across a range of disciplines, observations, and informal interviews conducted over three trips to Bangladesh, we have applied mechanical engineering design methodology to develop eight key design strategies, which were used in the development of a low-cost, community-scale water treatment system that uses ARUBA to remove arsenic from drinking water. We have constructed, tested, and analysed a scale version of the system. Experiments have shown that the system is capable of reducing high levels ofarsenic (nearly 600 ppb) to below the Bangladesh standard of 50 ppb, while remaining affordable to people living on less than US$2/day. The system could be sustainably implemented as a public-private partnership in rural Bangladesh.