Archeological studies indicate water deer was once distributed among much broader range than currently during the Pleistocene and the Holocene periods; records have been obtained from eastern Tibet in the west, Inner Mongolia and northeastern China in the north, southeastern Korean Peninsula (Holocene) and Japanese archipelago (Pleistocene) in the east, southern China and northern Vietnam in the south.

[14] Water deer also inhabited Taiwan historically, however this population presumably became extinct as late as the early 19th century.

[15] Water deer are indigenous to the lower reaches of the Yangtze River, coastal Jiangsu province (Yancheng Coastal Wetlands), and islands of Zhejiang of east-central China, and in Korea, where the demilitarized zone has provided a protected habitat for a large number.

[16] In China, water deer are found in Zhoushan Islands in the Zhejiang (600–800), Jiangsu (500–1,000), Hubei, Henan, Anhui (500), Guangdong, Fujian, Poyang Lake in Jiangxi (1,000), Shanghai, and Guangxi.

[18] Water deer inhabit the land alongside rivers, where they are protected from sight by the tall reeds and rushes.

An introduced population of Chinese water deer exists in the United Kingdom and another was extirpated from France.

[citation needed] The majority of the current population of Chinese water deer in Britain derives from escapees, with the remainder being descended from many deliberate releases.

It appears that the deer's strong preference for a particular habitat – tall reed and grass areas in rich alluvial deltas - has restricted its potential to colonize further afield.

The main area of distribution is from Woburn east into Cambridgeshire, Norfolk, Suffolk and North Essex, and south towards Whipsnade.

[27] On April 1, 2019, a water deer was spotted using a photo trap in the "Land of the Leopard" national park in the Khasan district of Primorsky Krai, Russia, 4.5 km from the border with China.

[citation needed] The coat is an overall golden brown color and may be interspersed with black hairs, while the undersides are white.

[34] This has implications for the conservation of the different populations, especially as Hydropotes inermis is classified as Vulnerable in its native range according to the IUCN Red List.

Sometimes a small pit is dug and it is possible that in digging, the male releases scent from the interdigital glands on its feet.

The male also scent-marks by holding a thin tree in his mouth behind the upper canines and rubbing his preorbital glands against it.

The fight is ended by the loser, who either lays his head and neck flat on the ground or turns tail and is chased out of the territory.

Tufts of hair are most commonly found on the ground in November and December, showing that encounters are heavily concentrated around the rut.

[35] Females do not seem to be territorial outside the breeding season and can be seen in small groups, although individual deer do not appear to be associated; they will disperse separately at any sign of danger.

During the annual rut in November and December, the male will seek out and follow females, giving soft squeaking contact calls and checking for signs of estrus by lowering his neck and rotating his head with ears flapping.

[citation needed] The doe often gives birth to her spotted young in the open, but they are quickly taken to concealing vegetation, where they will remain most of the time for up to a month.

Once driven from the natal territory in late summer, young deer sometimes continue to associate with each other, later separating to begin their solitary existence.