This book aims to analyse the feasibility of using rainwater from the Alto dos Franceses Condominium, located in the municipality of São Luís/MA, for non-potable purposes such as garden irrigation and floor washing. To this end, the catchment area of the roof, the rainfall index recorded in the municipality and the water demand for the common areas of the Condominium were considered. The various elements of the system were dimensioned, such as gutters, conductors and the reservoir that will be used to store rainwater.