There are many various interpretations, meanings of the snake. India, China, and Japan it has been associated with water and the river gods. Popular snake tattoos the cobra and dagger/snake tattoos are representative of the venomous elements of a snake.
One of the most popular snake tattoos is called ouroboros. mentioned in the Book of the Dead, in art, the snake forms a circle with its tail in its mouth. In the renaissance, it symbolizes eternity time and the universe. A combination of snake and tree, male and female respectively are said to have formerly symbolized fertility. In earlier days the snake has been associated with sun worship.
There are many more varied associations and controversial meanings to the mysterious snake. In choosing a snake tattoo whether it be by itself or in combination, I would recommend doing some research if you want to inform yourself of the various meanings and interpretations.