There is such a thing as a "chinese watersnake" but that is not it. The chinese watersnake, Enhydris chinensis, is olive brown to gray with scattered black spots from the nect to the tail and has a white or kind of yellow lateral stripe along each side that make a sort of zig zag pattern. The belly is yellow or white and each ventral has a dark edge. It's mildly venemous but can't cause serious harm to humans (headache, nausea, etc). Some photos of it are on the webpage linked blow down at the bottom. Definitely not what your friend has but since it was sold under this name then it's worth knowing about.
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