Family : HOMALOPSIDAE
Species : Gerarda prevostiana
Maximum Size : 53 cm

References : H1, H3

Link : Aquatic Snakes of Southeast Asia, Field Museum of Natural History ... follow this link

Thanks to Sohan Shetty

This unassuming snake inhabits coastal habitats, particularly mangroves, where it feeds on small fish and soft-bodied crabs.

The dorsal surface is generally brown in colour, but sometimes greyish. The lower scale rows and ventral scales are white or pale yellow, as are the labial scales (those lining the lips) and chin. As with other water snakes, such as the Dog-faced Water Snake, the head is barely distinct from the body, and the small eyes are located towards the top of the head. 

It ranges from India, Sri Lanka and Bangladesh to Burma, Thailand, the Malay Peninsular and Singapore.