They need a land area and a water area (and enough space). They must be able to get out of the water or they'll get shell rot. Make sure the level isn't too close to the top or they might climb out. Try to make sure they can't get caught or tangled in any water decorations. They will sometimes eat smaller gravel rocks which is not good. They also need quite a bit of daylight (or UVB) to process vitamins and nutrients and a proper diet. Good filters are really important as they can be very dirty which can lead to illness but changing water too often can do this as well. They need a heat lamp and submersible water heater (make sure you get something so you are able to tell the water temp.). It can cost a lot to set up a turtle the right way and they can live a long time when cared for properly which doesn't happen often enough. They can also carry salmonella so always keep that in mind and disinfect appropriately.
