Banded Water snakes are a stout bodied (unlike most Garter snakes) that occur through several southern States of the USA. They can be found generally in marshy areas, around ponds, lakes and streams and can be described as aquatic to semi-aquatic. They are non-venomous, although the bite of Nerodia species has been documented as an irritant and some people have taken a reaction.
In captivity a keeper needs to be mindful that if kept to wet or damp they this species may be prone to skin blister problems. The best way to alleviate this problem is to make sure good hygiene is maintained, and also that the snake has access to somewhere they can spend time to thoroughly dry out.
We would suggest a glass terrarium is best suited to this species. Provide a large water area to allow for bathing. Naturally planted tanks are sometimes used by some keepers. This can provide complications – the damp and wetness issue, and also the fact that the heavy bodied nature of this species, along with their activity levels will flatten all be the most sturdy of plants. For this reason it is suggested its easier to maintain them in a more artificial environment with artificial plants and décor.
A basking area, during the day should reach around 28-30C, and temperatures shouldnt drop below around 20C at night. Various heat 
sources work well, some prefer ceramic heaters, other prefer incandescent or halogen light bulbs. Lighting is best provided with a T5 UVB light, many use the Arcadia Shadedweller tube.
This species would naturally eat frogs mainly, along with fish. In captivity they can be “swapped” to eat rodents, but not all will do this. They are relatively active snakes, if feeding rodents once a week will enable this level of activity, if using fish perhaps every four or five days will be better.