Add 4 cups of water to a pot. Place the pot on the stove and heat the water. The water does not need to come to a boil.
Add 1 to 2 drops of peppermint oil per cup of water in the pot. Leave the pot on the stove and stir the mixture for a couple of minutes.
Remove the pot from the stovetop. Let it sit and cool for about 10 minutes. Use a funnel to pour the peppermint oil and water mixture into your spray bottle.