Background Surface runoff is generated by rainfall flowing over the earth’s surface. Urban development over recent decades has rendered land increasingly impermeable, as the soils of agricultural lands and woodlands have been replaced by asphalt and concrete. When rain hits these paved/sealed areas, water gathers pollutants that have accumulated on their surface to generate a polluted runoff stream. This type of contamination is known as non-point source, or diffuse pollution. It has an intermittent flow and a heavily polluted first flush runoff stream generated within 30 minutes of a rain event. This often causes flooding during heavy rains, as a result of inadequate or failing urban drainage systems. Uncontrolled discharge of runoff and stormwater in urban watersheds lowers the quality of receiving waters, making it difficult to keep concentrations of priority pollutants (such as heavy metals and pesticides) below levels set by the Environmental Quality Standards (EQS) Directive, and to achieve good status of water bodies set by the Water Framework Directive (WFD). To tackle this problem, Sustainable Urban Drainage Systems (SUDS) are being adopted for the management of runoff and to mitigate the effects of stormwater, in line with the objectives of the Floods Directive. Objectives LIFE DrainRain is to mitigate the environmental impact of runoff in water bodies (coastal, surface and ground waters). Currently, SUDS only drain runoff water and care needs to be exercised, as infiltration-type SUDS technology may pose a high pollution risk for groundwater bodies. The project takes this approach a step further, by coupling SUDS to treatment systems for diffuse pollution, especially making use of photocatalysts in pavements. In particular, the project will design and implement pilot systems of pervious photocatalytic concrete pavements to decrease uncontrolled water runoff and concentrations of priority substances such as heavy metals, polycyclic aromatic hydrocarbons, pesticides and polychlorinated biphenyls, with the aim of complying with Environmental Quality Standards, contributing to the protection of groundwater and the maritime environment. The project will also demonstrate the efficient use of water resources, defined as one of the top priorities of the European Roadmap ‘Maximisation of water re-use in the EU’, and will help to meet the microbiological quality needed for irrigation and other applications, according to the Spanish Water Re-use Regulation. The pilot runoff sustainable drainage and treatment system will consist of several components: A pervious concrete photocatalytic pavement with organic pollutants first treated on the concrete’s surface by the photocatalyst Titanium Dioxide; A drainage and distribution system in which water is collected by pipes made from anti-microbial materials; A hydrodynamic separator that utilises centrifugal energy generated by the water flowing inside to separate suspended solids and oils (SS); A filter that comes after the complete retention of SS by a pre-filter to avoid clogging, heavy metals will be removed by adsorption on support materials, such as activated carbon and lignite; and An anti-biofouling storage tank, which has been constructed using anti-biofouling high-density polyethylene (HDPE), for storing the regenerated water in a way that ensures microbiological quality.The project will demonstrate the system in two pilot plants in Spain with different climates (Oceanic and Mediterranean) to promote its wider replication. One area is 900 m2 of pervious concrete surface area in the seaport of Ferrol (Galicia) and the other in Calasparra (Murcia) covers 150 m2 of road hard shoulder. Expected results: Reduction in the microbial load of runoff water due to the antifouling and antimicrobial treatments included in the DrainRain system, resulting in a decrease of microbial contamination (below detection values); Decrease in the concentration of oils in the water by 95%; Improved groundwater quality by increasing the drainage of inorganic pollution-free runoff water; Re-use and recycling of runoff water for uses such as irrigation, car washing and cleaning of public walkways. According to the dimensions of the two pilots and expected rainfall, runoff volumes of 913 and 460 m3/year will be treated and reused in Ferrol and Murcia, respectively; Reduction of direct discharges of polluted water into marine environments, leading to a reduction in the high levels of industrial pollution suffered by rivers and estuaries with major shipbuilding and port activities, as in Ferrol; Minimisation of the risk of flooding and its impacts by reducing runoff flow rate; Promotion of the development of sustainable drainage separate systems, through the inclusion of a runoff water treatment system independent of centralised wastewater treatment systems, and thus increased performance of those by reducing peak flow rates; Reduction of the air pollution by capturing Volatile Organic Compounds and Nitrogen Oxides and thereby also improving air quality by photocatalysis; and Mitigation of the heat-island effect in urban areas.