Separated Stormwater
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Problem
In most older cities, stormwater and sewage share the same pipes. During heavy rain, the combined system overflows, dumping raw sewage into rivers and lakes. The problem is invisible — literally underground — and the solution requires separating the clean water from the dirty water before they ever meet.
Evidence and Discussion
Separating stormwater at the lot level — handling rain where it falls, through rain gardens, permeable surfaces, and infiltration — reduces the load on the combined system and keeps clean water out of the sewer. Philadelphia, Copenhagen, and Melbourne have all demonstrated that lot-level separation is more cost-effective than pipe replacement.
Therefore
handle stormwater on-site wherever possible. Route roof runoff to rain gardens or cisterns, not to the sewer. Use permeable surfaces for all non-structural paving. Ensure that no clean stormwater leaves the lot through the sanitary sewer connection. In new construction, install separate storm and sanitary connections. In existing buildings, disconnect downspouts from the sewer and route them to rain gardens or infiltration areas.