Collapsible Water Bottle
I have one of those camel pack things, which I bought for a mountain climb, and they are aweful. This looks the same, except it has a lid where the tube would screw on.
The camel pack makes water taste worse than swimming pool water, and is a nightmare to clean. It also involves sucking on a tube to get water, which is more effort and can actually leave you breathless. Useless on a mountain.
This looks too similar and easy to rip or puncture. My caution would be to not buy!
I plastic bottle uses a lot of space, therefore this collapsible water bottle has some merit. I think the tubes, hose, etc. is a bad idea.
I do not recommend this bag, however, it does have some uses. I think to buy a separate backpack just to carry this collapsible water bottle is close to as nuts as you can get. People continually worry about weight and what do they do, they buy extra items of no use.
The idea of sucking while walking and become breathless is a problem. I wander what the bike people think, the true Velo Sports types, do they want the weight on their backs or do they want the bottle holder on the bike?
Camelbacks for travel seems goofy to me. If set up right, no suction is required, you just bite on the valve and it almost flows out. For some uses, they are invaluable, these would be when you need to keep hydrated but need your hands free (soldiers on point etc). I have used these on motorcycles. For this purposes, a soda bottle attached to the bike, with a hole in the bottle cap and a hose going to it are perfect. No bite valve necessary.
But if possible it is always better to stop. I have seen hikers with these systems and I just don't get it. A soda bottle is lighter, indestructable, and free. A water bottle is even lighter. Some hikers use Nalgene bottles. Why? These are heavy, hard to drink from while moving and expensive.
As for the collapsable bottle, these work great if you want to keep your pack space more empty but occasionally want to have a lot of extra water and don't want to go out finding a larger soda bottle or you want more pack space as you use it. This can be if you are hiking where there is plenty of water for most of the hike, but on occasion you will need to carry more. This is infrequent.
The type you show is pretty good, but if full the edges can wear through some packaging/fabrics as it is a little stiff.
The only real use I have found for these, with the tube, is when I am on a motorcycle that I cannot attach a water bottle to and do not want to stop. I put one of these bottles in my tank bag and drink from the tube. Kept clean it will not change the taste of the water like some of the camelbacks and will not leak.
To carry 2-3 liters at one time?
Of course this depends on what I am doing? Balance in the biggest problem with water, it weighs a lot, so whenever I go to the mountains I always seem to be the one carrying three or four bottles for the weaker bunch.
I do not carry a 5 gallon collapsible as it would slosh around. I would carry 2 bottles or 4 bottle, would not really want carry unless I had room in my pack and nothing else.
I often just put a cord around the neck of the bottle, make a noose in a way, and hang them down my front as a counter balance to the backpack on my back. I do not carry two bags on a trek
I have to keep the bottles from swinging. However this much water could be put in the pack, close to the back, or closest to my back, so the center of gravity is closer to my body. I semi like the bottle on top of the bag, not on the bottom with my butt hanging.
Planning for water is an interesting thing.
When I was in Iraq, they people froze bottles of water and brought along, I thought this a good idea.
To tie together bottles would allow you to loosen one bottle, drink it, share it, then allow you to rebalance your bag.
Bottom line is bottles, or this plastic collapsible bottle would be good, if for a long trip, I would buy the one liter, not the two liter, and lots of them.
I tested some soft bottles by Platypus and was really impressed with how leak proof they were. I threw them in my purse with all kinds of keys and pens that I thought for sure would spring a leak and they held up great - and there was no leaking even when I used the bite valve top.
I agree that soft bottles are tricky to clean - I've been using a mix of baking soda, water, salt and a little white vinegar - just drop in the dry stuff with a small spoon and pour the wet stuff in. The fizzy reaction makes it a little easier to clean, then I just rinse it with water.
You can check out Platypus bottles here: http://www.reusablebags.com/store/platypus-c-169.html