Water for a Red Ear Slider

You can't just plop them in tap water. The chlorine will kill them. Get some of the treatment drops sold for aquariums and use that to treat the water they will be in for living and feeding. Also, they are very suseptible to catching colds, and colds are often fatal to small turtles. You should have some means to keep the tank warm, either an undertank heater or a bulb. They also need sunlight to manufacture vitamin D, same as you, and should spend an hour or so each day dry and in the sunlight.

Turtles can drownd, though usually it's due to being trapped and unable to rise for a breath. Be careful not to leave tight hidey holes in the tank, they get in and can't get out.

Don't feed your turtle hamburger, under any circumstances. You can offer tiny bits of carrot, tomato, apple, mango, lettuce, and the like. They will develop a taste for their favorite things, and you'll be able to tell what they like and don't like.

Although turtles have a bad rep for salmonella, unless you put them in your mouth it's not much risk. The turtle is far more likely to catch something from you that will be detrimental to their health. Handle them with clean hands, and afterwards wash your hands well with soap and water. Clean the tank well at least once a week, and rinse it well to remove the detergeant. You shouldn't see much mess unless you feed them in the tank, if you do that you will need to clean about every other day because turtles are really messy eaters. A bit of trivia- turtles eat their own poop, so you won't see any unless your turtle is really ill. Gross bit of info, but something to keep in mind.