While I'm not 100% sure, I ...
Published by Alexis Morgan, Water Stewardship Lead at WWF International
While I'm not 100% sure, I suspect USGS has some methods to do this as the Clean Water Act in the US has to tackle this issue so they've probably developed some tools and approaches. Otherwise you could also reach out to Microsoft and AI for Earth as they may have some tools that could map and compute this. Regards and best of luck!