Every turtle or tortoise requires a piece of land and water to survive. Here I will explain how you can fulfill that need.
Obviously, aquatic turtles need water--lots of it--to swim in. The absolute minimum depth of the water must be more than the width of the turtle's shell. Hold your turtle on its side and watch it as you pour water into the tank--its shell must be completely covered. If the water isn't deep enough and the turtle happens to flip over in the water, it won't be able to turn itself right side up and will drown.
More than that is usually better. Sliders, paints, and wood turtles much appreciate having space to dive and REALLY swim! However, mud turtles are poor swimmers, so the minimum or just slightly more water depth is best for them. Adult mud turtles should never be kept in more than 8 inches depth of water, and they must be observed to ensure that they do not have difficulty swimming against their filters' current. Snapping turtles are good swimmers but they prefer not to. Snappers would much rather sit on the bottom of the tank and stretch their long necks up to gasp air from the surface of the water. Therefore, the absolute minimum water depth is best for snappers of any kind. Alligator snapper hatchlings especially must be observed after filling their tanks because sometimes their necks are too short to reach the surface and you CANNOT give them less water than the minimum. If you see they have the mimimum water and still cannot reach up to breathe, they should be given a rock they can sit on and still be submerged but that is closer to the surface than the bottom of the tank.
A piece of land--however small--is also essential to survival at all. If a turtle has nowhere to clamber out of the water and rest, it will either use too much energy swimming up to the surface to breathe or will try to sleep floating in a corner. Turtles cannot get real sleep--dream sleep--if they are in the water. (They may doze or relax down there, but they can't really sleep!) Also, if their shells are not allowed to dry out from time to time, it will become a bacteria/fungi farm and will likely result in a serious case of shell rot. At the very least, the turtle's shell will lose its waterproof quality.
Therefore, aquatic turtles must have an area where they can get out of the water and get dry, or they will eventually die. This piece of land can be very small. A branch affixed at the water's surface under the basking lights will do. For very young hatchlings, the floating leaves of aquatic or plastic plants may do as long as they do not sink under the turtle's weight. You can make a "cave" out of stable stacks of rocks. Be creative!
There are, of course, commercial products for this purpose. I particularly like ZooMed's floating turtle log, as it works both as a place for the turtles to hide and doze and a log for them to climb out of the water. Zoo Med's floating turtle docks also work great, and this was the only thing my blind red-eared slider could use. Big Apple's WaterLand tubs are also neat, as they are plastic tubs designed to be 2/3 water and 1/3 land with a nonslip ramp going out of the water. Same goes for their turtle tanks.
The land and water porportional requirements for the brackish terrapins are the same as for aquatic turtles, so please read above.
However, there is the question of whether to keep terrapins in salt water or fresh water. The answer is both! Terrapins' bodies are able to filter the salt out up to a certain amount, then after that they will stop drinking until they can get fresh water to flush their kidneys. However, the salt water helps to treat shell rot and is more "native" to them so may be better for newly acquired or sick animals.
So, the thing to remember is, if you keep your terrapin in salt water, you must take it out and soak it in fresh water for about 10 minutes once a week to allow it to drink. Those 10 minutes are sufficient for the whole week. If your terrapin is wild-caught or if it is captive-born but is experiencing shell rot, it must be kept in salt water. However, captive-born terrapins that are raised in freshwater seem to do well in unsalted water. I currently have one terrapin living with a couple of sliders in freshwater and she is doing very well, but I also have an extra tank available should she get shell rot so I will be able to treat her in salt water.
Apparently the best level for salt water is a gravity of 1.018. After about 6 months, wild-caught terrapins can be acclimated to a gravity of 1.014 to 1.016. Captive-born terrapins who are experiencing shell rot can be kept in water with a salinity level anywhere within the 1.014 to 1.018 range. Please test it with a hydrometer! Adding rock salt is an inexpensive and effective way to raise the salinity level of tap water. To lower it, simply replace some of the water with freshwater.
Semiaquatic turtles, pretty much, can be kept either as aquatic turtles or as semiterrestrial turtles. For example, there is much debate over whether wood turtles should be kept as box turtles or as aquatic turtles. From much research, apparently South American wood turtles do well in a semiterrestrial setup while North American wood turtles do well in an aquatic setup, but there are turtle breeders who say they keep either either way, so who knows? It seems to be a case of the individual turtle's preference.
I would compromise. I'd provide the turtle with lots of land and a shallow walk-in water bowl, just like the semiterrestrials. But I'd also give them a place to swim. In an outdoors enclosure, you could accomplish this by sinking a 50-gallon rubbermaid tub into the ground or by making a ramp into a kiddie wading pool or something similar. Indoors, this may be difficult to achieve and will require creativity. If your turtle is not too large, Big Apple's Land Waterland tub may work as it is 2/3 land and 1/3 water with a nice nonslip ramp leading out of the water.
However, if you are already keeping your semiaquatic turtle in either an aquatic or semiterrestrial setup and it is happy and doing well, then there probably is no need to change it. If it ain't broke, don't fix it...
Semiterrestrial turtles live on land, but they need lots of moisture. If they don't get it, their skin will get very dry and their shell will shed off. They may get a white flaky fungus on their limbs. Especially hatchling turtles or Western box turtles will dry out like a potato chip and get severely dehydrated.
So, they need a place where they can walk in water and get completely wet...The opposite of aquatic turtles! These turtles should have a nonslip water bowl that is deep enough to wade in. (It's very important that the water bowl is nonslip, or if the turtle should happen to flip in it it won't be able to get a grip and turn itself back over and therefore will drown!) The water should come up to the turtle's chin when its head is pulled in up to its eyes. This is their comfort level. For my 5 to 6 inch Eastern box turtles, this is about 1-1/2 inches deep.
They also need adequate humidity. This can be provided by giving them a place to burrow. I'll explain this into more detail on my humidity control page.
Arid-land tortoises have basically the same requirements as semiterrestrial turtles. However, they need a drier environment, so as not to cause pneumonia. (This will be discussed on my humidity control page.)
Because of this, many books and resources say that arid-land tortoises do not need water, that they get all their water from their food. Sadly, this is not at all true!!! It is understandable why people believe this because my own tortoise never seems to use her water bowl--in fact, seems to be afraid of water. However, after letting the bowl sit dry for 2 days, I observed her run over to the bowl and bury her head in the water and drink long and deep! In addition, wild tortoises have been found near running streams. They also make use of puddles and dew when available in the wild. They do drink water!
Some tortoises truly do not drink, but even these tortoises have access to microclimates in soil in the wild that keep them hydrated. We cannot provide our tortoises with such microclimates in perfect simulation, so soaking our tortoises every 3 days or so is essential to ensure they do drink. Also it has been said that providing the tortoises with a wade-in dish with a shallow "puddle" in it that they can soak themselves in encourage them to drink more than a bowl will.
I have noticed, though, that my tortoise prefers more shallow water than my box turtles. She prefers more of a puddle than of a place to wade in. For her, I fill the water so it comes up to the rim of her carapace. That way it's deep enough to allow for easy drinking but it isn't a swimming pool. That is, for my 5-inch Russian, about 3/4 to 1 inch deep.
Some arid-land tortoises also have another need. It is said that tortoises will not urinate until they have fresh water to replace it with. It is believed that in the wild tortoises urinate after a good rain. Therefore, it may be essential to get your tortoise completely wet from above to simulate this. For outdoor setups, you could spray the tortoises with a garden hose for a minute or two. Indoors, you can gently trickle water over their head. A tortoise's nostrils are connected directly with their mouth and many will instinctively raise their head up into the "rain" and take in water this way. I have noticed this more with wild-caught tortoises--captive-born ones seem to enjoy soaking themselves more and don't seem to need this. It is still advised to soak all tortoises occasionally by taking them out into a bowl of shallow, baby bath warm water and keeping them in that for 20 minutes. Once or twice a week should be sufficient to ensure that an adult tortoise is properly hydrated.
It is important that you know what kind of animal you have so as to fullfill its needs properly. Do so, and you will have a very happy and healthy pet to hand down to your grandchildren!
