text: how are ulraviolet rays used to treat water? explanation required in detail with diagrams showing how water can be disinfected/purified using ultraviolet rays. i think you should do your own homework.  but, a good place to start is to understand the basic idea.  ultraviolet light is higher in energy than visible light, which means that it can cause damage to living cells.  this is why you get sunburned when you go out during a sunny day - sunlight also has some ultraviolet component and the damage done to your skin cells causes your skin to get red and tender.    since you are a big organism, the uv won't kill you - unless you stay out in very, very bright sunlight for a long time.  then you'll get seriously burned and probably get sick and possibly die from an infection.  however, a small organism like bacteria is usually only a single cell!  so the uv will damage their tissue enough to kill the bacteria.  good luck!