I keep garter and water snakes the same way. With a light bulb on a timer for heat and on a diet of half fish and half rodents. The rocks are set up in layers with spaces, so there's a heat gradient.

Although I am a fan of Diamondback, Brown, and Plainbelly Water Snakes, they get too big to keep in a 20 long set-up (like the ones pictured below). Devoting a 40 gallon or larger tank for their set-up would be beyond what I'm willing to do at his time.

The nice thing about Broad Banded Water Snakes is that they look cool AND have a relatively small average adult size (22-36 inches).

Tim

Third Eye Herp