The absolute best hydration bladder on the market. I've tried the camelbak, hitec, and outdoor products. I also had the original platypus and this one is a definite improvement with the blue sliding lock. Althought the original one never leaked, I was always skeptical. This one took the question out.

It's also easy to clean.

I've only tested this out at home, so I can't vouch for it's durability over time in tough conditions, but so far so good!
I was worried that the blue plastic piece across the zip opening would be cumbersome, and unnecessary weight, so I tested the bag without it. I was pleasantly surprised when the piece slid off easily when I tried to remove it, but I didn't get the feeling it would slide off accidentally. Once I filled the bladder up with water, I squeezed it and flipped it around to test the zip closure, and it didn't leak or show any sign of weakness. I also attached the drink tube (no leaking or dripping!) and taste-tested the water (tasted fine to me). When I took the drink tube off a small drop of water came out of it, but that was all. I saw no reason to worry about it dripping significantly or squirting when taking the tube on and off, which is a relief.
I bought the 3 liter/100oz to put in an Osprey Atmos 65 pack, and it fit fine. This is the largest size recommended for that pack, and the top did stick out a bit from the hydration reservoir, but mostly because of the blue sliding piece (which can be removed).

The last time I used a camelbak it leaked all over and it was hard to get water thru the mouthpiece. The Platypus Big Zip SL worked great the first time I used it and I would buy it again.

This is the first time I used a Platypus water reservoir and it worked great. No leaks and the mouthpiece actually worked the first time. I really had to struggle with my last camelbak mouthpiece.

this is great because like the name suggests, the top zips off. Its essentially a giant zip lock bag. It makes it really easy to scoop up water from a river and then add purifying drops to it. I don't feel as if it will ever come unzipped as it clicks into place, and I am never worried about losing the top because its connected to the bag. very nice bladder all around

In 5 years, I have been through 5 water packs, until I got this one. The removable tube is helpful when you are filling the pack because you don't need to pull the tube through the hole in your pack to free the whole unit. You can simply clip the tube back in and stuff the water pack into your pack.

My main problem with previous water packs is that they leaked, not necessarily within my pack but from the spout/mouthpiece. So far I have taken this one on dozens of trips, including travelling abroad, and have had no issues with leaking. The locking feature on the mouthpiece obviously helps this.

Finally, the elastic cord attached to the piece that zips the unit closed means that you won't lose it or drop it. It fits snug and secure, and again, has not caused any leaking yet.

Highly recommended if you want to stay hydrated while you are on the move.

I recently got the Platypus Big Zip SL bladder in the 2.0 liter size to put in Patagonia's 750 cu Endurance Pack, primarily for mountain biking. I thought that the basically glorified zip lock bag design would be good for easy filling and drying out. (I always like to get my hydration bladders as dry as possible so strange things don't start growing...) I also liked that this bladder comes with a shutoff valve and 90 degree bend for the mouthpiece, unlike with CamelBak which sells the bladders and shut off valves separately unless you buy their whole backpack. The piece that makes the drink tube removable does add a bit of bulk, but with a bulkier mouthpiece and shut off valve, it is nice to be able to route the tube in the other direction and just leave it there. It also gives the added bonus of helping the tube dry out more quickly when it is detached. For now I'm pleased, though I'm wary of so many "extra" parts that could break. All the more reason to get this through Backcountry because of their sweet return policy. I guess only time will tell. I know people who prefer the Platypus mouthpiece to CamelBak's, but for me it's taking a bit of time to get used to. Overall, I think it's a neat design, and if you're looking for an alternative to CamelBak's bladders, I would definitely recommend you give this one a try.

It doesn't leak, it sits well in the daysack and I could refill it without having to take the bladder, nevermind the drink tube, out of my bag - major plus. The 2L was perfect size for a 15L daysack.

In the next version, include a cap so that we can hygienically cover the mouth piece when not using it.

I picked this up after doing a lot of research on bladders. I found that the ease of use with the Big Zip was pleasing. I usually like to sway away from the trends so I didnt go with Camelback. I have nothing but posistives to say about this bladder. It zips closed well and the quick disconnect tube is very nice! I have a Osprey Kestrel 48 and it fits nicely and works very well. I would recommend this to anyone!

Putting ice in the platypus bladder is easy and I like the bite valve a little better over the Camelbak's.

Great high quality hydration bladder. I've never had any problems with anything from Platypus. You don't get that plastic taste like you do with Camelbak. Very easy and efficient to use, the tilted spout makes it easy to drink out of when it is in a pack. Also the detachable hose makes it so you don't have to wind it through all the holes etc. just to take it out. The best feature though is the zip top, makes it extremely efficient to fill up. No more screwing on tops or messing with other closures, just put the top on and zip, it's closed. Never had any leaks.