Problem with UV is that maintaining minimum exposure time is critical to the process and light-on isn't good enough indication in itself. OK if there is proper control of the flow though the unit, but a little too high and you don't have good water.
We only use it for drinking water from a drinking water system that only passes less that 1/2 gallon per minute. We are not filling large jugs or trying to run a lot of water through it. The one we have is only one gallon per minute of purification but you can get larger units and they are not that expensive either. We know lots of other people use these. I do understand about the flow rate and our system is designed not to exceed the flow rate - in fact well below the flow rate. But anyone who is worried can buy higher flow systems. None of them cost very much. We also use the series of filters I mentioned previously - lots of filters. To each his own - just trying to point out that things are available to provide clean drinking water for those who might like to know.