Size and Compatibility
The first thing to consider is if the hydration bladder will fit the compartment in your backpack. Most hydration bladders use a similar shape but they all vary a little bit. More important is the size. Almost all bladders come in two-liter and three-liter sizes, and some come in even smaller sizes (1 liter = 33.8 ounces or a little more than a quart).
In general, we recommend 3L hydration bladders. Compared to 1L and 2L bladders they are about the same price and weight but give you 50 percent more water. You can choose to fill your bladder the whole way or just part way. One reason not to get a 3L bladder is if the compartment in your pack is small. For example, in trail running sports, a running pack like the Salomon ADV Skin 12 Set will typically only hold a 2L hydration bladder. That said, you can still use a 3L hydration bladder, we just can't fill it up the whole way. If you're looking for something versatile, go larger, but if you want a bladder for a specific purpose, find out what size your pack will best accommodate, and get that. Take a look below at our sizing guide to help guide you in making a size decision.
Even though we recommend a larger bladder, it may not be in your best interest. Take a gander below to see which size is best for you. All bladders we tested had large and small reservoir options.
1 Liter (or 1.5L): A great size for minimalists, commuters, or kids. It's perfect for quick hikes and trail runs, or if you intend on filling up often on the trail (if you're out for a day or more).
2 Liter: Probably the most popular option. This is best for those taking off for a day hike, ski, or snowboard into the backcountry. If you're not a fan of constantly filling up, this is a great option. It provides a sufficient amount of water for most of the day (depending on how thirsty you are!)
3 Liter: The most versatile of all sizes. This is perfect for those who don't plan on filling up or are in need of a lot of water. We like this size the most because you have the option to carry a lot or a little water. Many of our backpackers found this to be a sufficient size when going through areas with little to no fill up opportunities.
Another compatibility consideration is the profile of your bladder. Some bladders are wide while other are narrow. Some (when filled) are fat while others are flat. So what do you need? Before you purchase a reservoir, take a look at your Hydration Pack. Most that are hydration bladder compatible come with a built in sleeve. Take a look at the sleeve to see how wide or narrow it is. From that you'll be able to determine which bladder to choose. In general we preferred long and narrow bladders like the HydraPak Shape-Shift Reservoir. This particular profile fit into most packs and felt flesh against our backs.
How much should you plan to drink daily?
In general, we recommend 17-25 oz of water per hour for hydration during endurance activities. The range is dependent on the air temperature and your exertion level. Here is a great article on hydration and exercise. We generally take 18 oz an hour for most activities (more when it gets hot). Based off this metric, you can determine how much water you should plan to carry (if there are no water sources to fill up).
Hydration Bladder Opening: Zip Top, Fold Top, or Screw Cap?
When considering what kind of bladder opening to go with, you need to consider how easy it is to fill, the environment you are filling in, and how easy it is to open and close. There are three styles of bladder openings: fold top, zip top, and screw top.
Fold Top bladders were the most popular in this review. The tops flip up and folds over; once folded over, you slide a closure over the top and the bag is free from leaks! We found this to be the best type of bladder opening when filling up in streams or other outdoor environments where you need to gather water from limited sources. We also thought they were great to use under a regular tap at home. We loved that we could turn most of these inside out to clean and really get to the hard to reach places. Bladders that use this opening include our Editor's Choice the Geigerrig Hydration Engine and the Hydrapak Shape-Shift Reservoir.
Zip Top bladders are similar to the fold top style. They resemble a large ziplock bag with a closure that fits overtop the zipper. Even though these are easy to use, many of our testers thought they took a little longer to open and close then fold top styles. These bladders are also great options for filling up at slowly flowing streams and at home under a regular tap. Even though they are easier to clean than screw top options, we found them harder to clean than fold tops as you needed a brush and could not flip them inside out. The Platypus Big Zip LP was the only bladder tested that uses the zip top system.
Screw Top bladders take a little longer to open and close than zip top or fold top versions but were the easiest to fill in shallow basins. The screw models are held horizontally or diagonally when filling, which allows them to be easily filled in a sink or water fountain. This is especially handy at public restrooms and camping restrooms where you often don't want the bladder touching more surfaces than it needs to. You can also completely top them off, whereas with flip and zip top closures you usually have to leave a little air at the top to close it without spilling. That said, we had some trouble cleaning screw top versions as there were hard to reach nooks and crannies. The MSR Dromlite Bags and CamelBak Crux Reservoir are both screw top hydration reservoirs.
Bite Valve Size
Bite valves vary in size and type and most feature a locking mechanism. Some are larger while others are smaller. The size of the valve affects how easy or hard it is to suck water from the tube. In general we found that bite valves that were larger where harder to suck water through the tubes (except if you had a pressurized system). Small valves were sufficient, but didn't offer the larger water flow that medium valves provided. These medium valves featured in the CamelBak and MSR models were our favorite.
For locking mechanisms, there are two types, the turn valve and the switch. We recommend the switch as they were easier to clean and easier to use while exercising. These valves are found with CamelBak, MSR hydration kit, and Platypus models. Unfortunately, turn valves were harder to use and often get stuck if not cleaned properly after using sugary drinks.
Even though we have preferences with bite valves, we found that most reservoirs have interchangeable tube and valve options. So if you prefer a certain type of valve/tube but love the reservoir, simply change it out.
Ease of Cleaning
Cleaning hydration bladders can be a nightmare. Most hydration bladders have some place that is difficult to clean and dry, making it perfect candidate for bacteria take-over. Bladders vary wildly in how easy or difficult they are to clean. If you only put water in a hydration pack, you don't need to clean it that often. However, if you use sugary sports drinks you will need to get the sugar residue out almost every time you use the bladder. There are three main areas to clean: the hose, bladder, and mouthpiece. When purchasing a bladder, consider how easy or hard the bladder is to clean. Look for a wide mouth so you can either flip the bladder inside out or easily fit a brush inside. Make sure you can disassemble the hose and mouth piece easily. Many bladders come with a quick-release mechanism that allows you to disconnect the hose from the hose. If a bladder doesn't come with this function, keep in mind it will be VERY difficult to clean the hose. In general, we found flip top bladders that could be turned inside out and thrown into the dishwasher were the easiest to clean. We'd also recommend checking out some cleaning tablets like the Hydrapak Bottle Bright, which are non-toxic and free of chlorine.
Pressurized or Not Pressurized
A pressurized hydration bladder has two chambers: one for the water and one for air. Using a pump, you can blow up the air chamber to create a pressurized reservoir. This means that the water will squirt out of the bite valve without needing to be sucked. At first we were a little skeptical of this technology because it seemed like it was solving a problem that didn't exist. We have found that pretty much all hydration bladders are easy to drink out of and you don't really need assistance. However, through our testing we found the real benefit of pressurized platters is that they allow for a whole lot of novel uses in the field. We used our pressurized Geigerrig hydration bladder to take a sun-powered shower, get water to our dog, clean off our dog after it jumped in a puddle, gently moisten our newly planted vegetable garden, and clean off dishes efficiently while camping.
Another upside claimed by Geigerrig to pressurized systems is that they will keep your tubes cleaner, more bacteria free and require less cleaning because no backwash can go up the tube. We were not able to verify this in our testing but it intuitively makes sense. That said, if you used sugary sports drinks, you will likely need to clean out the tubes whether your system is pressurized or not. Sugar residue is nearly impossible to get out of tubes without either massive amounts of flushing with warm soapy water and or by using a brush.
When considering a purchase, make sure your bladder is equipped with a quick release mechanism in a vertical orientation. Most hydration hoses connect to the bladder with a quick release mechanisms that make the bladder easy to fill and clean. Most manufacturers also use the same system that are compatible with one another, which means you can replace your hose and bite valve with whichever one you like the most.
That said, we noticed that some hoses weren't compatible in the orientation of the quick release mechanism. Some are orientated horizontally with a specific attachment, while most are oriented vertically. For example, the Platypus Big Zip has a quick release mechanism that is anatomically compatible with others, but it is orientated horizontally, while others are orientated vertically. As a result, when you plug in a different hose (that is usually orientated vertically), it sticks out to the side instead of sitting up and down. This can result in durability issues in the long term. Make sure your bladder has a quick release that is orientated vertically if you plan on switching them out. If you don't plan on switching them out, don't worry about it!
When temps drop below freezing, there is a good chance the water will freeze in your hydration tube and mouth piece. A good tip in the winter is to blow water back into your main bladder and clear the hose after each sip. You can also buy winterized tube kits that cover the hose in neoprene. This insulates the hose and prevents it from freezing.