Contaminate

You create a nasty poison that is harmful to ingest and infuse it into either food or water. You can contaminate up to 10 gallons of clean water or food for up to 10 people. Anyone who eats or drinks for the contaminated batch must make a Con saving throw. On a failure, they take 3d6 poison damage and are considered poisoned, or half as much on a success with no additional effect.

You can also contaminate one healing potion and convert it into a potion of poison instead.

At higher levels. When you cast this spell using a spell slot of 4th or higher, you can increase the amount you can contaminate by 5 gallons of water or food for 5 additional people for every level above 3rd