Treat rain as a resource, not waste: Glasgow forum compares four places’ approaches

A day-long forum at the IWA World Water Congress in Glasgow on 6 October looked at managing rainwater nearer to where it falls, treating it as a resource rather than waste.

The “Managing Rainwater Where It Lands” forum compared how Australia, Flanders in Belgium, San Francisco in the United States and Hamburg in Germany approach rainwater, asking what legislative and regulatory barriers had been overcome and what measurable benefits resulted. Julia Buckley MP gave the keynote, and speakers included Celeste Morgan, Bert de Winter, Paula Kehoe and Franziska Meizinger. The forum’s stated aim was to produce recommendations, and delegates were expected to make commitments for future action.

The four places the forum compared use very different tools.

Hamburg: a charge on every square metre

Hamburg’s RISA programme — “rain infrastructure adaptation”, developed by the city’s environment authority and the utility Hamburg Wasser — has produced a structure plan intended to guide how authorities, planners and residents handle rainwater. The city backs it with money. Its split wastewater charge bills rainwater separately: €0.83 a year for each square metre of sealed surface that drains to the public sewer, with green roofs and grass pavers counted at half. A rainwater tank of at least 2 m³ cuts the chargeable area by 20 m² for every cubic metre of storage; Hamburg Wasser’s worked example puts the saving for a 2 m³ tank serving 100 m² of sealed surface at €33.20 a year. Grants cover 40% of private rainwater-storage costs, up to €1,500, and half the cost of infiltration systems for households, up to €25,000.

Flanders: rules that doubled

Flanders relies more on regulation. Its 2023 regional rainwater ordinance, which applies to permit applications from 2 October 2023, sets a hierarchy: collect and reuse rainwater first, infiltrate what remains on the property, buffer it if infiltration is not feasible, and only then discharge it separately. The ordinance lowered the threshold at which an infiltration facility is required from 250 m² to 120 m² of draining surface, doubled the minimum infiltration area from 4% to 8% of that surface and raised the minimum volume from 25 to 33 litres per square metre. Local rainwater and drought plans map where infiltration, buffering or reuse make sense.

San Francisco and Melbourne

San Francisco requires qualifying developments to submit a stormwater control plan using measures such as bioretention, rainwater harvesting, permeable paving and green roofs. Its utility, SFPUC, also pays for larger projects: since February 2019 its Green Infrastructure Grant Program has awarded about $29.65 million to 29 projects. Grants of up to $2.5 million are available for schemes that manage at least half an acre of hard surface and capture the 90th-percentile storm of 0.75 inches.

In Melbourne, planning controls require developments to meet best-practice stormwater targets — cutting typical urban loads of suspended solids by 80%, phosphorus and nitrogen by 45% and litter by 70%. Melbourne Water’s 2024–25 outcomes reporting records 74 new stormwater treatment wetlands handed over by developers, although a 2026 analysis found Victoria is still falling short of its stormwater-flow targets.

A pioneer honoured

Separately, Professor Han Mu-young, emeritus professor at Seoul National University, received IWA’s Contribution Award in Water Resources Management and Science at a presidential dinner in Glasgow on 3 October for his work on rainwater management, Chosun Biz reported. His best-known demonstration, the Star City development in Seoul, stores rainfall in underground tanks for toilet flushing, landscape irrigation, firefighting reserves and storm detention.

Why it matters in England now

The forum met with England in drought. In its latest weekly report, for 25 September to 1 October, the Environment Agency said 10 of its areas were in drought status and the rest in prolonged dry weather. In August the government said almost three-quarters of England was in drought, and the Environment Agency has estimated that England needs around 120% of average rainfall over the next seven months to emerge from drought by spring.

Keeping rain where it lands addresses both sides of that problem — less runoff in storms, more water retained for dry spells. Wales has required new developments to have their drainage approved by a SuDS approval body since 7 January 2019. England has yet to put the same statutory regime fully into force.

Reported from the IWA World Water Congress & Exhibition, Glasgow, 6 October 2026.

Written with AI assistance from IWA’s published accounts and the cited sources; the session facts were confirmed to The Stratawire at the congress. The illustration is AI-generated and is not a photograph of the event.