OP was mentioning water catchment, it's about preserving water from rainfall so it doesn't go straight into roads, gullies, rivers and oceans. It's not only abo

OP was mentioning water catchment, it's about preserving water from rainfall so it doesn't go straight into roads, gullies, rivers and oceans. It's not only about preserving water but also preventing problems downstream like flooding. SF already offers rebates on installing rainwater barrels and cisterns https://sfpuc.org/learning/how-you-can-help/rain-barrel-and-cistern-rebate https://sfpuc.org/learning/how-you-can-help/rain-barrel-and-... and there's a manual if you want to learn more https://sfpuc.org/sites/default/files/learning/RWH_Manual_Final-APR2018.pdf https://sfpuc.org/sites/default/files/learning/RWH_Manual_Fi... Those things can be scaled up https://franciscopark.org/francisco-parks-rainwater-catchment-system-in-the-news/ https://franciscopark.org/francisco-parks-rainwater-catchmen... But nothing beats Tokio's Underground Discharge Channel https://en.wikipedia.org/wiki/Metropolitan_Area_Outer_Underground_Discharge_Channel https://en.wikipedia.org/wiki/Metropolitan_Area_Outer_Underg...