A canteen with dirty water is acquired by filling an Empty Canteen.

It must be boiled on a Campfire for 120 seconds to make the water clean.

Drinking a canteen with dirty water will quench your thirst less than clean water, and additionally will make your player sick

You can cure sickness using Herbal Medicine

You can also use dirty water to plant tomatoes by combining tomato seeds with dirty water in the craft menu.