The state of Santa Catarina, southern Brazil, has been suffering from water scarcity mainly over summer due to high potable water consumption and outdated water supply system. On the coast, several cities have their population doubled due to tourism during summer. In this context, this paper aims to evaluate the potential for potable water savings by using rainwater in the residential sector of 60 cities located in Santa Catarina state. Computer simulations using the Netuno computer programme were performed considering long-term daily rainfall time series for each city and typical characteristics of houses such as roof area, number of people per house, potable water demand and non-potable water demand (rainwater demand). In total, 2,700 simulations were performed. From the computer simulations, an ideal rainwater tank capacity and the corresponding potential for potable water savings for each case were obtained. Results showed average potable water savings ranging from 75 to 461 litres/day per house and rainwater tank capacities ranging from 1,000 to 16,000 litres. Despite the production of average outcomes using long-term daily rainfall data in cities with a high inter-annual variation of rainfall, results showed that the use of rainwater in houses may bring considerable potable water savings in Santa Catarina state and so could contribute to mitigating the potable water shortages.