Hi there, there are good and bad bacteria, so continuious sterilization isn't necessary nor a good idea unless it is a Rx to recover from a specific disease or infection.

More importantly, using UV will likely drop a lot of micronutrients out of solution and degrade the quality of your fertilizer. I like to run a cleaner system than most, but sometimes being a clean freak opens it wide for a real pathogen to invade and destroy everything. When you have somewhat of a biosphere going on, the competition between innocous, beneficial and the few bad microbes tends to stabilize against 'invasions'

Your need for water filtration depends on the quality and content of the water that you are starting with. Most people's tap water is ok, especially if you let it sit out a few days first. But some people have water that is very high in calcium or iron, and those are not going to evaporate out like the chorine/chloramine water treatment chemicals.