Adding essential oils to the drinking water of a pet or animal can be very beneficial. By ingesting the oil in this manner, they are deriving the therapeutic value of the oil. Also, essential oils taken orally in the water can do much to help oxygenate the body. It is very difficult for disease to take root in a well oxygenated environemnt.
When your pet starts drinkng water with essential oils in it, it is best to dilute the oil as much as possible. It would be wise to add 1 drop of oil to a 1 liter glass bottle of water. Then add one capful (less for smaller animals and birds) of this diluted water to your pet's bowl and fill bowl with pure water. (BTW, never put oils in plastic containers. Use glass, ceramic, or non-reactive coontainers.)
Conifer oils and oils such as clove might be too strong to use in the drinking water of most animals, especially if they are new to the oils. Peppermint water, while great for some animals in the heat of summer, may be callenging for those animals that may bathe in their drinking water such as birds, and reptiles. When you are first introducing oils to your pet, it is best to start with a gentler oil or blend, such as Citrus Fresh.