My back ground in producing ultrapure water for semiconductor processing doesn’t apply much to killing microbes in water taken from puddles and pond to make it safe for drinking in the Mad Max world. I would boil the water in that case or use one of those hiker/backpacker filters from REI.
To check out the effectiveness one might use the counting of colony forming units on agar dishes of before and after treatment samples. Contamination during sample application is an issue. One of the scientific supply companies can furnish this gear; I have never bought these supplies myself so no recommendation. But boiling works.
Stock piling clean water before the FUBAR event might also work.