[RetroTechie]

> If you grow vegetables in an urban environment the rain will bring a lot of undesired things in any case.

Apart from areas with heavy air pollution, rainwater as it falls from the sky is generally clean enough that it's safe to drink. Almost anywhere on the planet.

But! As soon as it hits a surface, it's easily contaminated with anything & everything: bird droppings, lead (used as an additive to zinc) from galvanized corrugated steel, etc etc.

Basically: in most places, rainwater is as clean as the collection surface / piping / storage equipment used.