- For large firefighting devices, see Deluge gun.
- For the Australian species with a similar common names, see Mertens' water monitor and Mitchell's water monitor.
The water monitor (Varanus salvator) is a large lizard native to Southern Asia. Water monitors are one of the most common monitor lizards found throughout Asia, and range from Sri Lanka, India, Indochina, the Malay Peninsula and various islands of Indonesia, living in areas close to water.
The Water monitor is a large species of monitor lizard. Breeding maturity is attained for males when they are a relatively modest 40 cm (16 in) and weigh 1 kg (2.2 lb) and for females at 50 cm (20 in). However, they grow much larger throughout life, with males being larger than females. Most adult specimens will not exceed 1.5–2 m (4.9–6.6 ft) in length. However, the species can attain a maximum size of 3 m (9.8 ft). The largest specimen on record was an animal measuring 321cm from Ceylon (Sri Lanka). A common mature weight of Varanus salvator can be 19.5 kg (43 lb). The maximum weight of the species is over 50 kg (110 lb). In exceptional cases, the species has been reported to attain 75 to 90 kg (170 to 200 lb), though few such giants are verified and may be unreliable. They are the world's second heaviest lizard, after the Komodo dragon. Their body is muscular with a long, powerful, laterally compressed tail.
The generic name Varanus is derived from the Arabic waral (ورل), which translates as "monitor" in English. The specific name is the Latin word for "Saviour" denoting a possible religious connotation. The Water monitor is occasionally confused with the Crocodile monitor (V. salvadorii) because of their similar scientific names.
In Thailand, the local word for a water monitor "hia" (Thai: เหี้ย) is used as an insulting word for bad and evil things including bad persons. The word is also thought to bring bad luck, so some people prefer to call the animals 'ตัวเงินตัวทอง' - which means 'silver and gold' in Thai - to avoid the jinx.
The origin of this offensive meaning can be traced back to a time when more people lived in rural areas in close proximity to monitor lizards. Traditionally, Thai villagers lived in 2-story houses, the top floor was for living while the ground floor was designed to be a space for domestic animals such as pigs, chickens, and dogs. Water monitors would enter the ground floor and eat or maim the domestic animals, also hence the other name 'ตัวกินไก่' (dtua gin gai – chicken eater).
In Indonesian and Malay, the water monitor is called 'biawak'.
Subspecies of Varanus salvator 
- Asian water monitor, Varanus salvator salvator the nominate subspecies is now restricted to Sri Lanka where it is known as the Kabaragoya in Sinhala, and Udumbu in Tamil.
- Andaman Islands water monitor, Varanus salvator andamanensis: Andaman Islands; Type locality: Port Blair, Andaman Islands.
- Two-striped water monitor, Varanus salvator bivittatus: Java, Bali, Lombok, Sumbawa, Flores, Ombai (Alor), Wetar and some neighbouring islands within the Sunda arch, Indonesia; Type locality: Java (designated by Mertens 1959).
- Black water monitor, Varanus salvator komaini: Thailand. Type locality: Amphoe La-ngu, Satun Prov., Thailand, and Thai-Malaysian border area. This was formerly a subspecies, but now regarded as a synonym of V. s. macromaculatus.
- Southeast Asian water monitor, Varanus salvator macromaculatus: Type locality: Siam (Thailand). Mainland Southeast Asia, Singapore, Sumatra, Borneo and smaller associated offshore islands.
- Ziegler's water monitor, Varanus salvator ziegleri: Obi Island.
- Yellow-headed water monitor, Varanus marmoratus, and Varanus nuchalis were classified as subspecies until 2007 when they were elevated to full species.
Behavior and diet 
Water monitors can be defensive, using their tail, claws, and jaws when fighting. They are excellent swimmers, using the raised fin located on their tails to steer through water. Water monitors are carnivores, and have a wide range of foods. They are known to eat fish, frogs, rodents, birds, crabs, and snakes. They have also been known to eat turtles, as well as young crocodiles and crocodile eggs. Like the Komodo Dragon, they will often eat carrion. Water monitors have been observed eating catfish in a fashion similar to a mammalian carnivore, tearing off chunks of meat with its sharp teeth while holding it with its forelegs and then separating different parts of the fish for sequential consumption. There was a 2005 documented case of a mongoose trying to take a fish meal from a Water Monitor. The mongoose is quarter the size of the lizard. The lizard won what turned out to be a fatal contest.
In Hong Kong, it is a protected species under Wild Animals Protection Ordinance Cap 170. In Malaysia, this species is one of the most common wild animals around with numbers comparable to that of the population of macaques there. Although many fall prey to humans via road kill and animal cruelty, it still thrives in most states of Malaysia especially in the shrubs of the east-coast states such as Pahang and Terengganu. In the east-coast states of Malaysia, this species is very common in roadkill. In Thailand, all monitor lizards are protected species.
- The biology of water monitors Varanus salvator in southern Sumatra | Bushmeat Crisis Task Force. Bushmeat.org (2007-01-22). Retrieved on 2012-08-22.
- Pianka, King & king. Varanoid lizards of the world. 2004
- Malayan Water Monitor – Varanus salvator. Ecologyasia.com. Retrieved on 2012-08-22.
- Water Monitor Lizard (Varanus salvator) at Pak Lah’s House | Mutakhir. Wildlife.gov.my (2012-02-23). Retrieved on 2012-08-22.
- Water Monitor – Varanus salvator : WAZA : World Association of Zoos and Aquariums. WAZA. Retrieved on 2012-08-22.
- Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. ISBN 978-0-85112-235-9.
- Robert George Sprackland (1992). Giant lizards. Neptune, NJ: T.F.H. Publications. ISBN 0-86622-634-6.
- Netherton, John; Badger, David P. (2002). Lizards: A Natural History of Some Uncommon Creatures—Extraordinary Chameleons, Iguanas, Geckos, and More. Stillwater, MN: Voyageur Press. pp. 140–141. ISBN 0-7603-2579-0.
- Koch, A., M. Auliya, A. Schmitz, U. Kuch & W. Böhme. (2007). Morphological Studies on the Systematics of South East Asian Water Monitors (Varanus salvator Complex): Nominotypic Populations and Taxonomic Overview. pp. 109–180. In Horn, H.-G., W. Böhme & U. Krebs (eds.), Advances in Monitor Research III. Mertensiella 16, Rheinbach.
- "Soterosaurus: Mindanao Water Monitor". monitor-lizards.net. Retrieved 20 March 2012.
- Whitaker, Rom (1981) "Bangladesh – Monitors and turtles". Hamadryad. 6 (3): 7–9
- Stanner, Michael (2010). "Mammal-like Feeding Behavior of Varanus salvator and its Conservational Implications". Biawak 4 (4): 128–131.
- "Species Diversity, Distribution and Proposed Status of Monitor Lizards (Family Varanidae) in Southern Thailand". The Natural History Journal of Chulalongkorn University (Chulalongkorn University) 1 (1): 39–46. 2001-08. Retrieved 2009-06-28.
Further reading 
- Bennett, Daniel 1995 The water monitor Varanus salvator Reptilian 3 (8): 15–21
- Das, Indraneil 1988 New evidence of the occurrence of water monitor (Varanus salvator) in Meghalaya J. Bombay Nat. Hist. Soc. 86: 253–255
- Deraniyagala, P. E. P. 1944 Four New Races of the Kabaragoya Lizard Varanus salvator. Spolia Zeylanica 24: 59–62
- Pandav, Bivash 1993 A preliminary survey of the water monitor (Varanus salvator) in Bhitarkanika Wildlife Sanctuary, Orissa Hamadryad 18: 49–51
- Media related to Varanus salvator at Wikimedia Commons
- Animal Diversity Web
- The New Reptile Database
- Photos – Water Monitor Swimming