Whether you just bought your first backpack that didn’t come with a water reservoir (aka water bladder or hydration reservoir) or your existing reservoir has started to leak around the hose, at some point you’ll be in need of a new water reservoir.

Over the years, the reservoirs have gotten a facelift, making it easier to wash and dry them and providing more robust solutions to attaching them to your pack.

Here’s a quick list of things to look for when shopping for a water reservoir.

Size

This is the most fundamental decision you will need to make: How much water do you want your reservoir to hold? You’ll need to think about where you hike, how long you hike and the size/space in your pack.

For a frame of reference: If you hike in a dry, hot climate like the Grand Canyon, the National Park Service recommends you carry 4 liters of water per day. That may sound like a lot, but I myself drank nearly that much on a Grand Canyon hike along the Grand View trail so that number isn’t excessive.

Water reservoirs most commonly come in 70 ounce or 100 ounce (3 liter) sizes though you may find smaller ones or variations on those numbers. In my case, I use a 100 ounce reservoir and will simply fill it less full if I know I’m going on a particularly short hike. For longer ones, like the Grand Canyon, I’ll fill it and add two 32 ounce bottles to my pack’s side pockets to make sure I have plenty of liquid for the day.

Opening

Less than a decade ago, every water reservoir out there seemed to have a hole big enough to easily fill with water, but not big enough to reach your hand inside. This made it very difficult to clean and dry the reservoir after use. I had come up with a rather convoluted method of hanging the reservoir upside down after emptying it with a wooden spoon inside turned sideways to hold it open and let it sit for more than week till it was completely dried. And even then, there was still the risk of just enough drops of water left to lead to mildew issues on storage.

Today, there are still some reservoirs sold with these smaller openings, but the majority have a “wide mouth” or “access port” that is big enough for you to put your hand inside. If you are shopping in person, you can test it out to see if your hand fits; otherwise, make sure the features list a wide opening for easy cleaning.

Shut-off valves

All water reservoirs have some sort of a bite-style valve so when you are hiking, you simply bite the end of the hose and suck to get the water. This valve should be perfectly fine for on the trail needs, however, having an additional shut-off valve to stop water from coming out of the hose regardless of biting on it is important for when you aren’t carrying the pack.

Why you ask? Pinching a valve to let out water can happen without your intending it to. For example, if you toss your pack in the back of your car with a full water reservoir and it just happen to lean over on top of the hose’s bite valve, you could arrive at your destination with more of the water soaked into your car’s upholstery than in the reservoir.

Additionally it’s a nice extra should the bite valve start to fail over time. I have had reservoirs as they were nearing their end of life start to drip ever so slightly from the bite valve while hiking. I was able to use the shut-off valve as a back up and get a longer life out of the reservoir than I would have otherwise.

Hose attachments (magnets, clips)

This is a personal preference: how do you want the reservoir hose connect to your pack while you are hiking? For some people it’s just slung over the should and swings loosely, others may have a built-in loop to hold it on their pack, or you might have a clip of some sort that comes with your particular reservoir or that you add on afterward.

For me, I use a magnet attachment that seems to only come on Nalgene- or Osprey-branded reservoirs. A built-in magnet near the bite valve connects to a magnet you add to your shoulder strap on your pack so when you drop the hose it simply snaps into place. After having a reservoir with this particular style of attachment I’ve never gone back to other types of clips.

Removable hose for cleaning/drying

Another handy feature for cleaning purposes is having a removable hose. I’ve had reservoirs both with and without this feature and would put it in the bucket of “nice to have” but not necessary. If you have a removable hose it’s much easier to really get every part of your reservoir dry before storing. Having said that, it does add complexity to the overall design and is one more place where you could have a potential failure or leak (though I have never experienced that in my reservoirs that have removable hoses).

Other features to consider:

• Insulation: If you plan to use your reservoir in extreme cold or snowy weather, you will want an insulated tube to add to your reservoir so that the drinking hose and bite valve do not freeze. You may also want to consider buying an insulated water reservoir
• Stability features: Some water reservoirs have stiff spines or added handles to help the water reservoir hold its shape when stuffed in a pack and not hung well.
• Hanging features: Your pack if it is designed for a water reservoir will have some sort of clip method build in to hold your water reservoir. Some use a single clip in the center, others have two side clips. Just make sure the reservoir you buy has the appropriate holes to hang from whatever clips your pack has. (most reservoirs are designed to be universal and work in any of the common pack designs)
• BPA/PVC Free: Newer reservoirs usually use non-leaching plastic material.
• Antimicrobial: You shouldn’t really need this if you are good about draining, washing and drying your reservoir immediately after use, but given how easy it is to forget to do this in a timely fashion, this may be a valuable feature to some people. (I’ve never sought it out in a reservoir and never had a problem).
• Baffle: This is a relatively new feature I’ve only just started seeing in stores. It’s basically a built in divider in the reservoir to help prevent sloshing of water as you walk. Alternative? Squish as much air out of the reservoir after you fill it and the sloshing will be kept to minimum without the need for a new feature.
• Screw lid: The screw lid on the port where you fill the reservoir varies by brand and in my experience is the most common reason for leaks (if not screwed on properly). Give a few a try at the store to see what is easier or harder to get in place straight and tight. While the functionality is the same with most reservoirs, the ease of use can vary.
• Buckles: A few reservoirs have buckles that make it easy to secure your reservoir outside a pack if desired.

My personal top feature needs:

• Wide-mouth
• Magnetic Clip
• 100 Fluid Ounce Size
• Shut Off Valve

My current water reservoir: Nalgene Get-A-Grip CXC Bladder, 3 L