Before having our pool built we did a lot of research concerning bacteria due to our daughter having cf. We are a family that loves the water and knows how good it is for all of our lungs, especially our daughters. Because of all the bad bugs in lakes and rivers we felt that a backyard pool was the way to go. The pool of our choice is an inground vinyl liner pool. We chose the vinyl liner because bacteria have a harder time adhereing to the vinly. It is also easy to keep clean. Gunite pools develope cracks wich grow many different algies. Some of which you can NEVER get rid of, even if you resurface. Fiberglass also gets cracks and bad algies. Don't get me wrong, vinyl can have bacteria but is easily cleaned and if needed easily replaced. My husband checks the chemicals in the water every day and keeps the pool super clean. Our daughter does better when she swims a lot. It helps to clear her lungs and it builds up lung function. A pulmonologist once told my mother that swimmers and people that play wind instuments have the best lungs. If you have a pool just make sure that you never let anyone swim wearing a suit that has been in a lake, river, pond, etc... No life jackets or toys of the same either, it will bring all the bad stuff into your pool and can take a lot to get it cleaned up again. Happy Swimming, Michelle