Rainwater saving and use in households, Bremen

Climate projections for Bremen indicate up to 44% more winter precipitation and up to 22% less summer precipitation by 2100, a temperature rise of up to 3.1 degrees C annually, more frequent extreme rainfall in winter, and increased flood risk from sea, river, rain and groundwater sources. These changes affect the design of the sewer system and increase the need for decentralised rainwater management, prompting Bremen to invest in it.

Establish a natural water balance and reduce rainwater discharge into the sewerage system by encouraging its reuse, while also cutting drinking-water consumption for uses such as toilet flushing.

Bremen combines a technical measure (subsidised rainwater cistern systems collecting roof runoff via gutters/downspouts for toilet flushing and garden watering) with an economic incentive (refund of the rainwater fee, 0.63 EUR/m2/year, charged on sealed area, if rainwater is used or the ground kept permeable). The investment subsidy covers up to 12,000 EUR or a maximum of one third of total installation costs; properties over 1,000 m2 must split the fee between rain and wastewater.

Installing a rainwater-use system costs at least 6,000 EUR depending on local conditions; the Federal State of Bremen's subsidy covers up to 12,000 EUR but never more than one third of total costs incurred. The rainwater fee (0.63 EUR/m2/year) is refunded where infiltration or use is achieved.

The funding scheme is identified as the main success factor, since without subsidies few homeowners take action despite stated interest in eco-friendly retrofits. Key barriers include cases where the system doesn't produce a net cost saving, owner reluctance about construction disruption (easier in new-build than retrofit), and high upfront investment costs, which the subsidy is designed to offset.