Solar powered UV light purifier
 

I had a thought while in an attic the other day. Why not use a solar tube light to sanitize my attic mounted a/c plenum? No power consumption, no bulbs to replace. Considerably more output than 14 watt fluorescent. Material cost is about the same for basic germicidal UV-c.

If there is any plastic in between the light and water it will block around 99% of the UV.
Then sun light allows other stuff to grow.