Piyush chlorine is not effective against Giardia or Cryptosporidium....
Apologies for going over this issue again in excessive detail. Each Trekker needs to decide what is the most practical, affordable and effective water treatment they are comfortable with using but try not to worry excessively about this so that it affects the enjoyment of the trek.
The published test reports indicate that various chemical water treatment methods like Chlorine in Piyush have verifying degrees of affect on those bugs, just not 100% under ideal laboratory conditions and less under field conditions so it should not be relied upon completely. It will deal with the majority of other potential microbial water problems so still worth using it. It depends on water conditions, temperature, physical particles and cloudiness, dosage and concentration, if you increase dosage enough, at correct temperature and for long enough it can have significant effect on the more resistant bugs. But these conditions and extra time may not exist while trekking depending on how the Trekker uses it and understands the issues such as at high altitude the water temperature is very low and all chemical methods react much slower, particles in water can reduce the effectiveness of chemicals and steripen, filtering does not deal with tiny virus etc. Even those using steripens that are 100% effective don’t seem to use clear water bottles to see if there are large particles that reduce the UV effect in the water before they decide to treat it.
In my last trek I used boiled water from lodge flasks and Piyush and did not get sick, maybe just lucky. In my clear water bottle there were many times where the bottom 10% had 20-50 black particles from 1-3mm in size, sometimes water was cloudy. This is to be expected as the water from black plastic pipes comes from streams next to lodges and the cloth filter on the tap can only reduce large particles but they have holes in the cloth so of varying effectiveness and would not filter bugs.
Even chlorine dioxide tablets which is the most effective, takes four hours to work on crypto bugs to be 100% effective, which is not practical as one needs to drink water faster on a trek. The only way around that is to have two water bottles to allow one to stand for 4 hours while the other is used.
So in reality there is no 100% practically effective method but all you can do is choose one that appears the most suitable for you in terms of the amount of effort and expense that you are comfortable with.
For my future treks I will try to use a combination of water from boiled water flasks in the lodges, filtering and chemical (Piyush, Chlorine dioxide or iodine based tablets) or steripen combined and will see if that is too complicated. The logic is that a clear water bottle allows you to detect large particles and cloudiness that interfere with chemical or steripen and one decides to refill from cleaner supply or to filter it, filtering removes large and small particles and crypto and giardia bugs (but not cloudiness) to allow the chemicals or steripen to work. I have had giardia at least 6 times over the last 30 years on treks and travels as I seem to react to them, while according to medical information 30% of people may get infected they don’t show symptoms, lucky for them.
Given the above comments, probably the most practical, cheap and effective method that is less mechanical failure prone is to have a clear water bottle with built-in filter, that one can treat with cheap Piyush chlorine droplets readily available locally, three levels of control with two step easy to use process in two packages (filtered bottle to drink from and chlorine droplets with 30 minute treatment time).
