I have a box in my gear room marked Water, and inside you'll find:
- 500mL wide-mouthed Nalgene bottle. Small enough to fit in the lid of my pack, this is what I carry 90% of my water on the trail in. At night it doubles as my mug, and with a screw on lid I can fill it with a hot drink and stick it in my jacket.
- 1L wide-mouthed Nalgene bottle. Only goes car camping and cragging with me.
- 16 oz metal insulated thermos. 16 ounces = rough 500mL. When its cold out, its easier for me (and my core) to drink hot fluids instead of cold. So for days out backcountry skiing, ice climbing, or mountaineering I'll carry a small thermos of instant cider or tea.
- MSR Dromlite 4L Bag. Having water on hand makes cooking a lot easier, so I'll bring along this 4L bag. If its particularly hot or if I'm going to be several hours between water sources (i.e., summit day on Mt Baker), then I'll use the bag too. I've found its easier to pack a 4L bag half full then a 2L bag filled full.
- MSR Hydromedary 2.5L System. I'm not a big believer in hydration systems, but I do think they have a niche. I never use one if the temperature drops below freezing - I've witnessed far too many problems with freezing. And I don't use them around sharp pointy things, like crampons and ice axes, because I've witnessed far too many punctures. I like MSR's model because its stouter then others, less likely to puncture, but I only use it when I don't want to stop for at least 3 hours. Otherwise I'd go with a Dromlite bag, which is more versatile.
- MSR Autoflow Microfilter. Another niche tool, great for car camping, base camping, or traveling with large (at least 4 people) groups. It holds 4L of water, which utilizes gravity (or a good squeeze) to push the water through a filter. When the filter starts to get gummed up, it can be quickly "blown out" by simply flipping it and running a full bag through to wash it out, then flipped back to normal.
- Iodine. This is my go to water treatment. Its small, simple, and effective. I don't have a problem with the taste - in fact, I'd argue that if you can taste the iodine strongly, then you've probably over-done it. One tablet for clear-looking water is sufficient, two tablets if you can see a lot of organic material floating around.
- Iodine. It simply lives in my pack, always available.
- Backcountry ski days, ice climbing. I'll simply carry the thermos. Done.
- Overnight backcountry ski tours, mountaineering. 500mL Nalgene, thermos, and Dromlite bag. If I wrap the nalgene in an insulating jacket, I can use it for another hot drink container. I rarely carry more than a liter at a time, so the Dromlite bag is for camp use.
- Cragging (roadside rock climbing days). 1L Nalgene is much less likely to get punctured. I'll bring two if its going to be hot.
- Alpine day climbs. Space is important - I want to carry the smallest pack possible. This is where the Dromlite bag really shines. Its easier to pack then a Nalgene and gets smaller as you drink. If it might be chilly, I may add the thermos. Maybe.
- Alpine overnight trips. 500mL Nalgene, Dromlite bag.
- Endurance days. The hydration system finally comes into play. Typically for me this is a trail run of more than 12 miles, depending on available water.
- Fastpacking (lightweight, 4mph backpacking). Hydromedary system again. I'll leave the Dromlite bag at home to save weight.
- Overnight trips with 4 or more (including me). Autoglow Microfilter. Not having to pump water really makes it worthwhile!
First, the disclaimer: I always provide water treatment for my guests. In smaller groups this is with iodine unless someone has an allergy to shellfish. If someone prefers not to use iodine due to taste, they're invited to bring a filter.
Now, watch me go out on this limb. I only treat my water a handful of times every year, since 1999, and I haven't gotten sick yet. This means that instead of carrying water, I simply stop and take a drink at "common sense" sources. My definition of a common sense source is one that I'm certain doesn't have heavy human use upstream - pastures, agriculture, camping, etc. If I don’t trust the water (because I see/know/suspect that there is a cow pasture/outhouse/water-treatment plant upstream), then I'll break out and use that bottle of iodine. Iodine is small, weighs little, and effective. Filter pumps work great, but take time to use, take up space in the pack, and add a significant weight to pack already loaded with climbing gear. Steri-pens work great too. But in my experience they stop operating in the field about 40 percent of the time, for a host of reasons that cannot be solved in the field, so everyone carries iodine as a backup. So why not just use the backup and leave the gizmo-technology at home? Now that I outed myself, let me repeat: I always provide water treatment for my guests. Whether or not they use it is a choice I leave to them.