The larger the tank is the better for the turtle. Do not go lower that a 35-gallon tank though. Only baby turtles can be kept safely in a smaller tank. Just remember that baby turtles will grow up so it may be best to just buy a big tank to begin with. You have a choice in the type of tank to buy. You can get a breeder tank or long tank, which is better than a high tank. These tanks will offer more space for your turtle.
Don't make the water level too high for the turtle. The turtle may not be able to flip over if the water is too deep it may drown. Also make sure that there is nothing on the bottom of the tank that can trap the turtle under water. If it can't come up for air, it will drown as well.
Because water turtles love to swim they need all the room that they can get.
Bigger tanks offer them the perfect place to enjoy this. They also eat in the water but will come out once in awhile to sit on a rock and sunbathe. It is important to create a swimming section and a dry land section in the tank. Since they love land as well, this will give them the best of both worlds. These sections don't have to be equal but should be sufficient for different activities.
Keeping the tank clean is extremely important to the health of the water turtle.
The whole tank should be cleaned thoroughly at each water change at least once a month. Don't wait until there is an odor or water discoloration and algae present before changing the water, do it consistently.
Take the turtles out of the tank as well as all accessories while cleaning the tank.
Drain the tank and wash it thoroughly with hot water.

Swimming Area
The swimming section of the tank must allow free swimming space so it is best to place the majority of equipment and accessories down along the borders of the tank. Equipment can be placed in the corners or under the dry land section.
Placing accessories around it can easily hide them. Do not put plants in the tank because your turtle will try to eat them and may become overfed.
Accessorize the tank with items that will not harm your turtle as it is swimming about. Talk to your local pet store to find out which items are best to put in the tank before rushing out and just buying anything that you think would look nice in the tank.

Dry Land Area
Raising the landmass above the level of the water can create dry land areas of the tank. In other words, by building it higher than the level of water in the swimming area. There are many types of materials available to help you do this.
Just remember that the size of the land area depends on the type of turtle that you have. Some turtles only need a small area to sun bathe or lay eggs, while others need more space.
The most important thing to remember when building a landmass is to keep the water from seeping in at the base to avoid a landslide and to create a small incline for the turtle to easily climb out of the water. A land section is a pleasant and practical addition to the tank especially if you plan to mate your turtles they will need a dry location for the females to lay and hide her eggs in.
Various items can be added to the land area for enjoyment by your turtle. Pieces of wood, like a small twig or smooth flat stones are perfect for sun bathing and are unlikely to damage the turtle's shell. Never put the tank in a location where the sun constantly hits it. The turtle could become overheated and die. It is best to place a basking lamp above the land area and also create some shady areas in the tank.
Mainly turtles thrive with a very basic tank arrangement. As long as the tank area is large enough so that the turtle doesn't feel confined, it really is not important on how you accessorize it. Many turtles prefer little or no accessories except a place to sit, dry off and catch some sun.

Lighting
As mentioned earlier, lighting is a very important addition to the habitat. Turtles need adequate lighting because turtles make their own vitamin D3 in their bodies by exposure to sunlight. This vitamin is needed to use calcium in their bodies effectively. Turtles usually get a portion of this vitamin from eating plants and animal substances. If they don't get enough light to produce this vitamin, they can get a bone disease or their shell can soften. Signs of a deficiency in vitamin D3 include sluggishness, anorexia, inflammation, shaking and weakness.
Just as important is the amount of calcium in their diets. If proper lighting is not made available to them, sufficient levels of the vitamin should be included in their diet as well.
Adequate lighting is needed for several major functions for turtles. It elevates their body temperature, it helps to prevent fungal infection by drying their shells, and it encourages good shell development.
You can use both a fluorescent ultraviolet B light and a warming lamp. The heat lamp provides warmth for sun bathing and the ultraviolet B lamp provides a way for calcium to metabolize.

Filtration
It is extremely important to keep the tank water clean for your turtle. Since your turtle will spend most of its time in the water, food decay particles and bodily excretions from the turtle can contaminate the water. If the tank is not properly cared for, your turtle can become very ill or even die.
Unnecessary illness can be prevented with proper filtration and frequent water changes. Bacteria can grow in warm moist places and the tank is literally a breeding ground for bacteria to grow in. If bacteria are allowed to grow in the tank, the turtle may experience problems with its shell or skin.
The frequency of water changes depends on whether or not you are using a filter and the amount of water that is in the tank. You should be able to see any waste in the water and should get rid of them before they decompose and contaminate the water. Regular water replacement or filtration can take care of invisible waste products.
If you use a filter you won't have to change the water so often. It will also prevent debris from floating around in the tank and being swallowed by the turtle. You will also need to keep the filter clean to keep it working properly.

Temperature
Because reptiles are cold-blooded creatures they rely on external sources to help regulate their body temperature. It is extremely important to maintain a constant temperature favorable to your in the tank that is favorable to your turtle. The following is the rule of thumb for water and land area temperatures.
• Water temperature should be kept at no less than 70 ° F and no more than 80 ° F. You don't want the water too hot or too cold.
• Land temperature should be kept at no less than 80 °F and no more than 90 °F.
• The temperature range at night will be different because you won't be using lighting sources then. A temperature range of 63 ° to 68 ° is ideal for nighttime.
Underwater heaters and basking lamps can be used to keep water and land temperatures within ideal parameters.

Accessories
Plants - You can add plants in your tank as turtles in their natural environment live among them. Be careful though as the turtle may try to eat them. Some plants may in fact be toxic to your turtle. Speak to someone at the pet store about proper plants for the species of turtle that you have.
An alternative is to use fake plants made out of plastic material. Make sure they aren't too flimsy or have jagged borders. When cleaning the tank make sure to clean any artificial plants since they can accumulate debris as well.
Stones - Addition of stones or flat rocks are vital to the habitat of your turtle. Not only do they allow for a place for the turtle to hide, but they also are useful in securing plants in the tank and forming inclines to the sun bathing areas. Make certain the stones are smooth all around to prevent injury to your turtle. Choose different shapes, colors and textures of stone for added appeal. Don't overcrowd the tank with too many stones since that will leave less space for your turtle to move around or swim in.
Gravel - Should never be used in the tank because your turtle could try to swallow it and choke. It also forms a breeding ground for bacteria to grow.
Seashells - Seashells can be added to the tank to add color and variety to the accessories. Don't put any shells in less that 1-inch though. Clean them regularly to remove any accumulated debris.
Wood - It is perfectly all right to put a small piece of wood in the tank for your turtle to climb on. You can also use a small twig.