Water monitors (Varanus salvator) have one of the largest ranges of any monitor lizard, living from India to the Philippines. Over this vast range, encompassing many islands and micro-populations, water monitors have adapted to a wide variety of habitats. Water monitors demonstrated their adaptability most effectively in 1889, when they were among the first vertebrates to recolonize the island of Krakatoa after it was destroyed by a volcano. This adaptability makes them hardy captives, and you can care for most varieties and populations similarly.
Water monitors are active lizards and require a clean, secure enclosure with an appropriate amount of space. Hatchlings need approximately 4 to 6 square feet of cage space, yearlings require about 20 square feet and adults need at least 30 to 60 square feet of space. Aquariums and commercial reptile enclosures are available to house your water monitor for the first few months of its life, but by the time it is 4 or 5 feet long, a custom-built enclosure is the only option.
Most authorities agree that monitor lizards do not require UVB; however, your lizard will benefit from quality, full-spectrum lighting, and commercial bulbs that produce UVB will not harm him or her. Some keepers prefer to light the entire enclosure, while others prefer to provide a bright end for basking and a darker end for hiding and sleeping.
Monitor lizards require heat lamps and access to a warm basking spot. Establish a thermal gradient in the enclosure so the water monitor has access to a variety of temperatures. A dome lamp fixture and incandescent bulb can be used to create the basking spot, though larger cages will likely need several fixtures to heat a large space. Place the lamps at one end of the enclosure. Use a non-contact infrared thermometer to measure the surface temperatures in the cage, and use a digital, indoor-outdoor thermometer to measure air temperatures. The basking spot should have a surface temperature of approximately 130 degrees Fahrenheit, the warm end of the enclosure should have an ambient temperature in the high 80s, and the cool end of the enclosure should be approximately 80 degrees.
Day and Night Cycles
One of the great debates of monitor husbandry involves the amount of light given to monitors daily. Historically, keepers provided their lizards with light-cycles approximating their natural habitat -- typically 12 hours of light and 12 hours of dark. However, in the early 1990s, a few keepers began experimenting with 24-hour lighting. The results have been very good, and a number of breeders have adopted the system. Others believe the constant light is stressful for the lizards, who need a dark period.
You can use a variety of substrates with water monitors. Organic soils, cypress mulch and orchid bark are all superb choices; they are absorbent, hold humidity well, and are generally safe for your lizard. Dirt makes an exceptionally good choice, as the lizards can burrow if they choose. Some keepers use newspaper, but the claws of an adult will quickly destroy paper substrate. Artificial carpets are a poor substrate for water monitors.
Provide your water monitor with a variety of hiding locations throughout the habitat. Water monitors will hide at night or whenever they're stressed or frightened. If exposed all the time, your monitor lizard will be stressed, paving the way to disease and a nasty temperament. Additionally, many keepers provide climbing branches for water monitors -- while adults may not climb as frequently, young monitor lizards feel safer in elevated locations.
Water monitors should be fed daily or every other day. Rodents and chicks should form the bulk of the adult diet, though occasional fish, eggs or shellfish can be provided. Young monitors should be fed crickets, superworms and small mice. Insects should be dusted with a high-quality calcium supplement every other feeding.