This is a fair point, however consider that failing to wash contaminants off your car/bike may (in certain circumstances) result in premature wear/rusting and result in you needing to replace componentry, or the whole thing with arguably heavier environmental damage (through extraction of metals and oil or gas for plastics, manufacture and distribution of components, as well as embedded fabrication energy). You may think that that doesn't matter because replacements are cheap, but they are only cheap because all the negative environmental damage is externalised elsewhere on the planet.
I wash my bike on my drive and make sure water goes into the guttering and drains, not the water table, where it is ultimately treated at some far off plant. Perhaps the lesser of many many evils.