To keep the water clean for long periods of time, we recommend adding either salt or hydrogen peroxide to the water. You can buy hydrogen peroxide almost anywhere online, just google it. For the salt solution, simply buy raw sea salt, or epsom salt and add around 1 pound (0.5kg) to a full tub. You can keep the water in the tub for 2-4 weeks when using salt. With no use of salt to disinfect we recommend changing the water every 3-5 sessions.