As rain offers a welcome relief to fire-scorched Australia, concerns over flash floods and freshwater contamination cast a shadow on the joy. Already, massive fish kills have been reported due to heavy ash and sediment in local stream.

Local reservoirs and municipal water supplies might become so polluted from the fires that the current water supply infrastructure will be challenged or could no longer treat the water.

Flash floods and water contamination after large-scale wildfires are emerging as real hazards in Australia and many other places, threatening drinking water, ecosystems, infrastructures and recreational activities.

In many ways, this is not surprising. Forests provide water to 90…