The bite valve on my Osprey water bladder is covered in a black mould.

enter image description here

It's not very old and this is the second valve I've had on this. It seems to be impossible to remove and seems to grow no matter what I do. Couple of questions:

  1. Is this likely to be a health issue?

    • I have used valves like this for long periods of time before so I guess not but would be interested to hear other options
  2. Does anybody have a good way to remove this?

    • Good old fashioned elbow grease doesn't seem to shift it (doesn't help that it's very inaccessible), nor does soaking in boiling water or disinfectant
  3. Can anyone advise how to prevent this from happening?

    • it seems to grow no matter what I do, though I admit I'm not very good at drying it out after every use...
  • 1
    Baby bottle sterilising solutions/tablets, follow instructions. Cheap and very safe Store the bladder and hose in the freezer when not in use and you won't have a problem with mould and other yucky stuff than can make you sick.
    – user5330
    Commented Dec 16, 2016 at 20:04

3 Answers 3


Ok so I've not had mine too long but this is what I do - bear in mind I'm not 100% sure what kind of the many moulds that is but I'd say it's probably not pleasant.

Vinegar should kill the mould. Mould stains, but it can actually simply be dead mould and has been treated. Leave it for a few hours and let it just seep into the valve.

Chlorine based cleaning products, such as the ones you use in bathrooms to remove the mould (kills and removes the stain) could, if you soaked it, remove the stain as well.

Neither of these would taste great (and chlorine isn't brilliant to ingest anyway, especially in the concentrations in household cleaning products), so you can then treat the valve with Bicarbonate of Soda, which you can pick up in any supermarket.

We use BiCarb to remove bad smells and the mould you get if you leave a water bottle for too long. I'd actually recommend trying this first to see if it'll clean it up.

Just be wary of chemicals vs the plastic, hence vinegar as an option, as you don't want to damage it.

I try to fully drain and hang up my bladder above a sink to let it drip dry after every single use - even if I plan to use it again the next day.

  1. Is this likely to be a health issue? No, it is very unlikely to cause ant health issues. This isn't mold, it's mildew. Mold should not be able to grow on silicone (the material of the outer sheath of the valve). Mold is a penetrating fungus, and needs a porous substrate to grow, this is why you've never seen mold on a window before. Mildew grows on surfaces that are damp and warm (like the inside of your valve). Mildew in these amounts is extremely unlikely to do anything to you at all. (Disclaimer: I'm not a doctor.)
  2. Does anybody have a good way to remove this? It should be quite easy to disassemble, and frankly I'm not sure why absolutely nobody answered this part. You want to pop the valve off of the connector like so...

enter image description here!

Next, you want to hold the silicone piece with one hand and push the little "button" on the end of the valve. enter image description here!

Your goal is to get the wide ring out of the little groove it sits in. Once you do, the plastic part will easily pop out. enter image description here!

At this point, you can just pinch the silicone bit and roll it between your fingers to loosen the mildew, then use a small brush and a bit of dish soap to clean it out. Reassemble, and Bob's your uncle.jm

  1. Prevention. Fungi are very particular about the pH of their environment. Back in the day we used to carry little vials of bleach in case we lost our filters or something like that, and of course bleach will kill anything, but it's not ideal since humans are included in "anything". Iodine tablets were also used for this purpose. Obviously neither of those are great options now, so you probably don't pack bleach but vinegar is quite useful to have, and if you just squeeze your valve and put a drop of vinegar in the valve it sho3uld prevent this happening (also potentially a fun gag to mess with fellow hikers if they didn't bring enough water).

This assumes you need to use the HydraPak continuously, if not just make sure to pop the mouthpiece apart when you're back from a hike and let it dry (but it sounds like this has been pretty well covered). You can also buy long thin brushes to clean your tubing, which will help prevent buildup in it, which will also help mitigate buildup in the mouthpiece.

Good backpacking gear should be easy to service and repair without any tools and—ideally—should be nearly indestructible. These are good gear (and they are priced accordingly 🤑).


There are cleaning tablets.

If you are lax on cleaning / drying that might not be the only mold.

They sell a cleaning kit. instructions


  1. Fill reservoir with warm water, do not use boiling water.

  2. Add one cleaning tablet to reservoir.

  3. Let dissolve for 5 minutes with the reservoir laying on its back.

  4. Shake the reservoir for 30 seconds to mix and spread the solution.

  5. Pinch the bite valve and squeeze the reservoir to remove air and fill the reservoir hose and bite valve with solution.

  6. Let reservoir sit for 15 minutes and then pour out solution.

  7. Rinse reservoir and tube with clean water.

  8. Follow directions for Cleaning Your Reservoir below for a deeper clean after these steps.


  1. Rinse out the reservoir and fill with warm water and a mild detergent, do not use Bleach or boiling water.

  2. Use the large brush from our Hydraulics™ Reservoir Cleaning Kit to scrub the interior of the reservoir.

  3. Remove the hose from the reservoir and the bite valve from the hose and use the small brush from our Hydraulics™ Reservoir Cleaning Kit to scrub the interior of the hose.

  4. Remove the silicone bite valve cover and clean it and the bite valve with warm soapy water.

  5. Let the hose and bite valve dry in a well-ventilated area.

  6. Insert the drying rack from the Hydraulics™ Reservoir Cleaning Kit through the cap and into the reservoir to hang and let dry and in well-ventilated area.

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