Yeah I think laws vary with each country. The UK drain/sewer/water treatment system was perfectly able to deal with the volume of home developing by amateur photographers in the 60s, 70s, 80s and 90s. Additionally chemicals designed for amateurs (all the readily available developers, fixers, stops, wetting agents etc) are designed to be OK to pour down the drain when finished with. The volume now will be much less than in previous decades....though I did check with my water company and they confirmed that "amateur" quantities of commercially available chemicals aimed at amateur photographers are OK to dispose of into the sewer system throughout England.
But I do hear that in some parts of the world either the sewage/treatment systems aren't able to deal with the chemicals, or rules have been introduced because the rule makers don't want to go into the decisions of what is safe and what isn't. I read of one case where a local law stated that "no chemicals may be poured down domestic drains"....so...no sugar in your coffee or you'll get arrested. Indeed no water down the drain either.