Hydration is an important part of chameleon husbandry--one that poses unique challenges for Canadian keepers. In what follows, I discuss how I understand hydration.
While dehydration alone can be fatal quickly, the ailments that come along with chronic low-level dehydration are just as serious. Kidney damage, prolapse, and a host of other problems can arise when a chameleon is not receiving sufficient water. However, constantly wet, soggy conditions creates a breeding ground for bacteria and fungi, and according to some, can be a recipe for a respiratory infection. So we have to strike a balance.
Urates and Hydration
Luckily, we have a pretty good way of diagnosing dehydration in our captive chameleons: their urates. When a healthy chameleon poops, their waste has two parts: the feces, and the urates. Feces tend to be brownish and urates will be white with varying amounts of orange. As urates sit in the body, waiting to be expelled, the body will reabsorb water from them according to its needs. As water is removed from the urates, they turn orange. So, a lot of orange in the urates indicates that the chameleon needed more water. Before you panic, please note that a certain amount of orange in the urates is perfectly fine. While I personally never see more than about 25% orange in my chameleons' urates, some sources say 15-50% orange is healthy and natural. One thing is for sure though, no orange in the urates is probably not natural. Some experts argue that this is an indication of over-hydration, which can be detrimental as well. Whether or not this is true, I think you are in the safe range if the urates are between 10 and 25% orange.
Ensuring our chameleons are well hydrated typically requires an integrated approach that combines several components. Misters, foggers/humidifiers and drippers are the most common fare in chameleon hydration; but like everything in this hobby, these tools are only useful if we understand what we are trying to accomplish with them.
Our current understanding is that (most) wild chameleons* experience fluctuating humidity levels throughout a 24 hour period; and, having evolved along side this natural fluctuation in humidity, have become masters of staying hydrated, even in areas that can go months without rain. To be sure, the natural cycle of humidity will differ from particular area to particular area, and since humidity is determined by the amount of dissolved water in the air relative to air temperature, humidity will also differ depending on the ambient temperature of different regions. However, the general pattern of humidity is as follows. As the sun sets, and the air cools, humidity slowly increases and chameleons settle in for the night. As the air cools to the dew point, the relative humidity approaches 100%, and sleeping chameleons are often surrounded by fog. As dawn approaches, leaves become covered in condensation in the form of dew. After spending the night in fog and near 100% humidity, chameleons wake up to dewy leaves from which they can drink if they so choose. As the day heats up, dew evaporates, humidity falls (often below 40%) and chameleons go about chameleon business. Then the whole pattern repeats. While there are certainly exceptions to this, this pattern is true for veileds, panthers and Jackson's.
*Like everything in this hobby, there are exceptions. Some deep rainforest species such as those from Cameroon enjoy high humidity 24/7.
Up to 30% of an organism's water loss is through simple respiration. When an organism breaths in dry air, that air absorbs moisture from the lungs, and is lost by exhalation. This is easily confirmed by breathing on a hygrometer. Of course, a lot will depend on how dry the air is: the drier the air, the more water will be lost to respiration. However, since air at 100% RH cannot absorb anymore water, it stands to reason that water loss through respiration will be effectively curbed in an atmosphere at 100% RH.
That chameleons sleep in such conditions, and have evolved to do so, suggests that this is an important part of how chameleons stay hydrated in the wild. Combine this with the fact that they can "top-up" their reserves by drinking dew from the leaves in the early morning, and we have plausible account of how wild chameleons stay hydrated.
What We are Trying to Accomplish
To be sure, the story is far more complicated than this, but we have enough information here to give a preliminary answer to the question of what we are trying to accomplish with the hydration tools mentioned above. By using tools such as misters and foggers, we are trying to provide our chameleons with the conditions they needs to keep hydrated. Those conditions are a nighttime atmosphere approaching 100% humidity, morning dew, and decreasing daytime humidity. This can be accomplished in a number of ways, but typically involves a good misting just before the lights come on, so the chameleon wakes up to a "dew-covered" enclosure. Misting just after lights out will create a humidity spike that a fogger or subsequent periodic misting will sustain throughout out the night. Adding a dripper for a few hours in the afternoon can supplement moisture without raising the daytime humidity. This may sound simple, and if you live in Florida, or Hawaii, it might be simple. But us Canadians have some unique challenges here. In particular, our centrally heated homes can dry the air out to less than 20% RH. Even with foggers, misters and humidifiers, sustaining an atmosphere of 100% humidity all night can be difficult. In the sections on enclosure types, and setting up an enclosure, I discuss some methods of addressing this particular challenge.
To be sure, something's being "natural" does not imply that it is best. However, replicating these particular natural conditions is how I ensure my chameleons keep themselves hydrated, and it works.
Until relatively recently, most keepers used the opposite approach to hydration. Several misting sessions were spaced throughout the day with a longer session first thing in the morning, and one in the evening. Experts and hobbyists argue to no end about which method is better--charging one method or another with causing respiratory infections, over-hydration, dehydration, and a litany of other ailments. My take on this debate is this: All sides agree that an enclosure needs to dry out daily. Otherwise bacteria and fungus can explode. Both sides also mist regularly and create very humid conditions at one or more points during a 24 hour period. The only point of contention is when to do this: during the day or at night? Given this, I opt for the latter because it is seems more consistent with facts about what chameleons have evolved to experience.
However, there are some species that have a reputation for being huge drinkers, such as Meller's and Parson's chameleons. There is some debate about whether these species are actually as thirsty as they seem, or whether the mere act of misting them causes a drinking response whether they need it or not. For folks who still want to be able to watch their chams get a good misting during the day, I recommend simulating a rainstorm by having all the lights go off for an hour in the afternoon. 15 minutes into this, you can provide a misting session. The idea here is that it is pretty unnatural to encounter heavy rain when its sunny out. Giving your chams a "warning" that a rainstorm is about to descend on them, allows them to prepare themselves.
In what follows I will discuss how particular pieces of equipment can be used in the hydration method I prefer.
These units can be used to fulfill several functions, and if your budget is tight, this is the first piece of hydration equipment you should purchase. If this is your only piece of hydration equipment, then program a ~5 minute misting session, just before lights on. Add another 5 minute session just after lights off, and follow that up with several 5-10 second sessions periodically throughout the night to maintain humidity near 100%. Remember, that it does not take very long for a fine mist to coat the entire enclosure. For brand recommendations see the section on equipment, and keep in mind that that water will have to go somewhere!
Cool Mist Humidifiers/Foggers
These can be useful tools for keeping the nighttime humidity up. The ones dedicated to reptiles typically come with a hose that can be directed right into the enclosure. However, it is easy to modify home versions as well. Try running them from midnight until lights on. A word of caution: bacteria and slime can build up on the inner surfaces of foggers and their hoses, and there is some debate about how this can negatively impact the health of our chameleons. To be safe, periodic cleaning of the accessible parts is recommended. (please don't use toxic substances that might become vaporized)
Whole Room/House Humidifiers
While I agree that low humidity during the day is actually optimal for chameleon enclosures, there are limits. If your house hovers below 20% RH on cold winter days, then a room or whole house humidifier might be a good idea. These will not be able to satify your chameleon's nighttime humidity requirements. You cannot raise the humidity of an entire room, or the entire house to 100% without inviting mold and other dangerous conditions. But to keep ambient humidity in the 30-50 range, these can be useful.
These are usually simple units, composed of a reservoir, a valve, and a hose. The valve is adjusted so a drop of water comes out every few seconds. They can be place above the enclosure and the hose directed towards a leaf that the chameleon can easily access. I use a more complicated version in all my enclosures, but I find the only takers are chameleons that I have recently acquired and are dehydrated from travel. After a few nights of 100% humidity and dew drenched mornings, they stop using the dripper.
An enclosure full of live plants will retain more humidity.