When my friends and I go backpacking we usually split one water purifier between two people. I would suggest someone else in the group picking one up. Typically it take 3-4 minutes to fill up a 32 oz water bottle. So if each person has two water bottles it can take awhile. Normally I do not carry a spare filter for the purifier, but if you are gonna use one purifier that much than you may want to carry a spare filter. Filters should last you several trips but it depends on how nasty of water you are filtering on how long a filter will last. Besides, what if for whatever reason your purifier is lost or broken. It is always nice to have a back up. So I recomend one per two people. That is just my opinion. As for Iodine pills, I am not a total fan of them except for as a back up. If your mixture is not correct you can make yourself sick, plus some of them really taste nasty. Todays water purifiers and filters are pretty good. You will not need any additional treatment to the water. Just pump it straight from the pond to your water bottle. Like I said previously, check to see if the one you are getting as an adapter to fit the bottles you use. It makes the process easier.