NeatWork is an advanced optimization and simulation tool for the design of purely gravity-driven water distribution systems aiming at delivering clean water to poor rural communities. The exclusion of any adjustable devices, such as pumps and valves, for controlling pressures and flows is motivated by two main reasons: firstly, the system should be as simple and as robust as possible to operate; secondly, the operating, maintenance and investment costs must be kept as low as possible, an absolute requirement in very poor rural communities. The challenge of designing such systems at minimum material cost is amplified by the random behavior of users. NeatWork proposes an original heuristic approach to the design of least cost purely gravity-driven systems under stochastic water demands. The concept of gravity driven distribution system has been used with success by the NGO APLV (Agua Para La Vida) for more than 29 years in the center of Nicaragua. The installed systems are still all in use and serve clean drinkable water to over 90 communities encompassing over 40,000 people. The user-friendly version of NeatWork first appeared in 2003 and is commonly used by the local technicians to design distribution systems at lowest material cost. In 2015 NeatWork and its successful use have been selected by the organization Water for Life (CMA) as the winner of the seventh edition of the Water and Sanitation Prize sponsored by the Inter-American Development Bank (IDB) and the FEMSA Foundation