Ultra Violet lights kill 99.9% of bacteria that could be present in water including e-coli, cholera and other harmful diseases. The water passes over a germicidal ultraviolet light housed in a high quality quartz sleeve. They come in various sizes and it is important to get the correct size for your requirements as if the water flows over the light to quickly it could be ineffective. The 11 watt is suitable for use with an under counter water filter while the 55 watt UV light is recommended for sterilizing the water with a whole house filtration system. Bigger sizes are available on request. Please contact us should you require more advice.