It is an N. sipedon sipedon. I've kept a few watersnakes. Their care is really no different from a king, milk, or corn, though a large water dish is a plus. UV is not necessary. They are very combative when caught but usually calm down quickly, especially if you don't let them spook you. They are naturally fish-and-frog eaters but can (and should) be trained to take mice.
I've found that wild-caught Nerodia are infection-prone; I suggest you get CB if at all possible.
I would agree with that...or alternately, treat them like a large garter snake. Agreed with getting them on rodents if you can, easier for you and the rodent diet is a lot less smelly both going in and out.