Monitor lizards vary greatly in their exposure to water in the wild. Some rarely encounter it whilst others never stray from it. Although many monitor lizards survive in the wild without ever drinking, a source of freshwater should always be provided for captives. However many monitor lizards, particularly desert species, will happily spend so much time emersed in water that their flesh begins to rot away. For this reason many people recommend that either the water receptacle for monitors from arid areas be too small to allow the animals to wallow, or else water should be provided just once a week. Eidenmuller (1993) notes that providing water for a short period each week, with the addition of a soluble vitamin supplement, helps ensure that the animals do not suffer from dietary deficiencies. Desert monitors are superbly adapted to conserving water but many aquatic species loose water at an incredible rate, and (hey must have constant access to a freshwater supply.
For monitors other than aquatic species, water is best provided in a heavy container that cannot be overturned. Some arboreal species (such as the emerald monitor) may prefer to drink above the ground, in which case a small water container should be securely attached In a branch. Some monitors may prefer to drink water from rocks or leaves. in which case a daily spraying of those surfaces with a fine mist should suffice. Even so a small receptacle of drinking water should always be available.
Water can harbour large numbers of potentially pathogenic microbes and so it is most important that it is changed everyday. Many monitor lizards like to defecate in water, adding considerably to its microbial load. Similarly any pools in the enclosure should be cleaned regularly and the water replaced every other day, or more often if needed. Allowing stagnant water to remain in the terrarium is asking for trouble. Never let water that has been in contact with turtles come into contact with the lizards. There is a very real danger of amoebic infection. Electricity and water are a lethal combination, so all connections should be sealed with epoxy resin and the apparatus equipped with a safety cut-off switch.
The humidity of the air in the enclosure is a very important consideration. Tropical forest dwelling lizards experience much higher levels of humidity than do those from more open. temperate areas. In general a relative humidity of 60-70% is suitable for temperate species. whilst those from tropical forests need a humidity of 75-85%. Seasonal fluctuations in humidity are common in the wild, with the highest levels achieved during times when both temperature and rainfall are high. The humidity can be measured with a simple hygrometer available from gardening shops. Pools or drinking bowls placed close to the heat source will generate significant humidity whilst misting the enclosure with a fine spray of water helps maintain suitable humidity levels. This is of benefit to all species during at least part of the year. Enclosures for monitors requiring very humid conditions must be waterproof and may have to contain drains in the bottom.
All monitors will immerse themselves if given the opportunity and many species not associated with water in the wild will spend long periods in it in captivity. Over long periods of time this can lead to fungal infections that eat away at the animals' appendages. Pools are only necessary for monitors that habitually spend time submerged in the wild. Although water monitors have been bred in set-ups with only small drinking bowls, the animals tend be more secure and less nervous if they can submerge themselves. For highly aquatic species (such as Mertens' goanna and the mangrove monitor) water should account for most of the volume of the enclosure.
A pool can be fitted into the false bottom of the enclosure to minimise splashes. The simplest way to make them is to use a fibreglass mould available from garden centres. Large pools require separate heating, usually by means of a submersible heater and thermostat of the type used for aquariums. A temperature of 20-28°C is suitable. All pools need very regular cleaning and the water should be replaced at least several times per week. Many monitor lizards can be given the occasional run of the bath, which is particularly beneficial during skin-shedding.
It is often beneficial to simulate rainfall. especially for tropical varanids. In order to do this the bottom of the enclosure must be fitted with a drain. Ideally the bottom of the enclosure can be made of mesh and the water collected in a large receptacle below (that must be emptied daily). The simplest way of simulating rainfall is to use a small aquarium water pump attached to a very fine spray bar. Special misters and automatic raining devices can be obtained from some reptile dealers. The water used should be 25-30°C and free from chlorine It is unnecessary to drench the lizards with litres of water, 10-20 minute showers are sufficient. Hot light bulbs often explode when splashed with water.
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