1. For what purpose? Chlorine will only work well if the water is relatively clean already. So although cheap, not very versatile.

There used to be a product called Polar Pure which was the only commercial available chemical (iodine) water purification product I know of. Unfortunately not available anymore. Also a big issue in storage, as it seems to effect things around it. (it even eats away at the Mylar coating, when stored in Mylar bags)

For long term storage, I would suggest a gravity water filter. I prefer Ceramic filter for this purpose, as they can be reset by scrubbing off the surface. They also don't have any issues with drying out (like hollow fibre type of filters). Gravity filter, because pumping is just a chore.

2. Good practise of use antibiotics is to:

Not use it, if it’s not needed.
- If you never let your immune system work, it will not perform well.
- You kill of the bacteria that are sensitive to the antibiotic, but there are always some of that harmful bacteria that are immune and survive. They will multiply and then you just got yourself a resistant bacteria.
- You will kill the good bacteria, some are needed for your digestion, some protect you from harmful bacteria.

If antibiotics are used:
- It’s best to check which bacteria if causing the infection and if they are resistant. Then take the smallest spectrum antibiotics, as they will limit their harmfulness to the good bacteria and prevent you from making bacteria resistant to the more powerful antibiotics.
- Always finish the prescribed course even when you feel better. If you don’t; there is a chance it will come back in a resistant form.

I would not self-medicate on antibiotics and certainly not preventively, as you have no idea what bacteria you are facing. So you won’t know if it’s effective, so you might be killing off the good bacteria that is protecting you when you need them. You don’t know how long to take them, but it will effect good bacteria and make bacteria resistant.

Antibiotic use is actually a hot topic and you can following a course about antibiotic on many MOOC platforms. (example this one just started: https://www.futurelearn.com/courses/antimicrobial-resistance-food-chain/1/todo/7301, although slighty different take, but still usefull for your generally knowledge)