Law No. 12.935 establishing regulations for flood control and the management of rainwater.

This Law establishes standards for flood control and rainwater management in the State of Maranhão by requiring new public and private developments with more than 500 square meters of impermeable surface area to install systems for the capture and retention of rainwater. Its main objectives are to reduce surface runoff and pressure on urban drainage systems, mitigate flooding and its associated damages, and promote the rational use of water resources by encouraging the reuse of collected rainwater. The legislation makes compliance with these requirements a condition for obtaining certain state approvals and licenses related to urban development, land subdivision, housing projects, and other large-scale undertakings. To achieve these goals, the Law establishes technical requirements for rainwater retention systems, including the installation of storage reservoirs sized according to a prescribed formula based on impermeable area and local rainfall conditions. It also provides guidelines for directing collected water toward infiltration into the soil, controlled discharge into public drainage systems, or reuse for non-potable purposes. Additionally, the Law encourages greater permeability in parking areas and integrates its implementation with Maranhão’s State Water Resources Policy and environmental management framework.