[UberRoo]

If you have any annoying pets or neighbor's pets, that's one way. (Two birds with one stone.) The other, and much more socially acceptable way, is to take it to an autoparts store. All my local Schucks stores take used automotive fluids free of charge. I don't know what other chains participate in a similar program. Your local waste management facility also should have a disposal station, and around here, it's also free. Both Schucks and the county waste management facility have limits on quantity and charge commercial users a fee.

To the best of my knowledge, ethylene glycol is environmentally fairly innocuous. It is readily filtered by groundwater systems and organically breaks down in pretty short order. I'm probably not supposed to recommend what I'm alluding to, but since most people spill more than they manage to catch anyway...

Oh, and my well water is more pure that most bottled water - but that's rare. Some minerals are bad, other are not. I don't have a complete list of which ones are which, and I sure have no idea which ones you might have in your water. The additives in antifreeze neutralizes a lot of the nasties that would otherwise plague cooling systems. I've never seen a cooling problem that could realistically be attributed to using dirty water.