My understanding is that germicidal/purification lamps work because they put out sufficient UV C to break down the cells of bacteria in the water. UV C is very bad for you because what it does to the bacteria, it will also do to you. It causes cancer.

It is a really bad idea to use germicidal/purification lamps. Alt processes generally only need UV A which is closer to visible light. UV A lamps are commonly available and fairly cheap (often labelled as black light or black light blue).