The clean-up instructions on the can of paint will tell you if your paint is latex or water based paint.

Paint discharge down drains or flushed into septic systems should be limited to brush cleaning waste. Paint should never be directly discharged down drains!

ALLOW THE PAINT TO DRY

Latex paint, when completely dried out, is not considered "hazardous waste". Find a well-ventilated area protected from pets and children to allow the paint to dry naturally. To speed up the drying process, add absorbent material such as kitty litter or sawdust or apply the paint to newspaper or cardboard.

When the paint is thoroughly dry, leave the lid off and place the container of hardened paint with your regular trash.