I got a fancy "double glass" cup, and put it in the dishwasher. Yesterday I noticed something really weird after the dishwasher finished the cleaning process:

water inside glass

As you can see, there are water "trapped" between the glass layers. The water won't go away when turning the cup upside down, neither when shaking it. I put it upside down all night, to no avail.

Any way to take the water out? (Without breaking the glass... ;))

8 Answers 8


My glasses are conventional borosilicate glasses which each has a tiny hole sealed with a hardly visible silicon plug on the bottom. Most double-wall glass coffee mugs are like that. When washed at too high a temperature in a dishwasher, the plug pops and dirty water enters. Do the following after slowly heating the glass in an oven to about 50°C to 60°C : With a syringe with a thin needle, extract all the dirty water as best as you can. Don't worry, you will never extract all the water. To clean the inside between the walls, next use the syringe to inject distilled water also at about 60°C that contains dishwasher detergent and shake and swirl to "wash the inside" and extract the wash water with the syringe. To rinse, now inject 60°C distilled water containing some rinse-aid used in dishwashers that allows drying through evaporation without stains. Rinse by swirling and shaking, then extract as much as you can of the rinse water, leaving the inside empty, but still with a few drops. Then "bake" the glass upside down (with the hole at the top to allow the remaining drops to vaporize to escape) until dry in an oven at about 60°C to 70°C, normally 8 hours. Once dry, and while still hot, seal the tiny hole with a tiny drop of hot glue from a glue gun. Fixed, but take care to never again wash the glass above 60°C in a dishwasher. Test if the seal holds with normal use when hot liquids are poured into the glass. Borosilicate glasses are designed for this and it's not the material at fault here, but the air inside that expands and pops the seal at high temperature. If your glass does not have that tiny hole at the bottom through which you can work with a syringe and needle, this method does not work. Use at own risk. Works well for me, but the hardest part is to get the drying stains not to show. Therefore, always use distilled water in the cleaning process, because ordinary tap water might contain calcium which when dried through evaporation, leaves a faint stain line. Fixed about three glasses this way, marriage is stronger than ever, now discovered vanilla-flavoured coffee syrup, and still going strong.

  • Good technique. To inject the water I use the syringe without a needle, held tight to the hole. To remove the water I shake out most of it, then use a syringe with a needle to remove what's left. To dry I bake at 120C for an hour. Not sure why you dry it below boiling temp? Also, after the distilled water + rinse aid I give it a couple of rinses with pure distilled water to reduce the amount of rinse aid between the walls. Not sure if that's necessary.
    – jay613
    May 17, 2022 at 19:32
  • Also if you drill out the old seal, hold the cup upright, drilling upwards, and drill very slowly, removing debris as you go. This will minimize the amount of dry silicone flakes between the walls that then need to be painstakingly rinsed out.
    – jay613
    May 17, 2022 at 19:52

The glass is already broken (or no water would have been able to get in). The break may seal at room temperature, and open up when the glass is heated.

To test this:

  1. Take a vessel that's larger than the cup, and fill this with hot water.
  2. Submerge the glass in the water, and see if water leaks in.

If water leaks in, the next step is to find the leak. If you examine the glass under a bright light, you may be able to see the crack.

Then leave the glass with the crack pointing down. If you keep the glass hot, the crack may open enough to allow the water to drain out.

You can try applying glass glue on the crack, but I don't see that holding very well. The glue should really be applied on the edges you want to glue together, not on the outside surface of the crack.

It's unlikely a repair will hold long, and (due to the uneven stress on the glass when it's used with hot liquid) chances are the glass will break completely if you use it again.

  • This is a great way to confirm that the seal is broken. Unfortunately, it doesn't solve the problem. Is there a way that the OP could utilize the broken seal to drain the water, and if so could you add that to your answer? Mar 5, 2019 at 14:55
  • 1
    @Brett if it's really broken then it's time to say good bye to the cup anyway, so the answer is useful even if not directly answering the question. :) Mar 5, 2019 at 15:42
  • @ShadowWizard Yeah, if the seal is broken then the cup would have to be carefully hand-washed, so I'd probably throw it away too. And the information in this answer is useful. I still think this answer should be a comment instead. Mar 5, 2019 at 17:00
  • The problem cannot be solved, the cup is beyond repair unless you've got a glass grinding set at home.
    – Hobbes
    Mar 5, 2019 at 17:41

Most of them should have tiny hole to balance the pressure and this helps to get the stuck water out. This article explains how to remove the water stuck in double wall glasses

enter image description here

  1. Make sure it is cold enough. (room temp is enough)
  2. Keep the water at that hole
  3. Fill it by hot water.

It should flush out!

enter image description here


Before throwing it away, it must be worth a try to put it in a warm, dry place like an airing cupboard and leaving it there for days or weeks.

In theory, the water will "boil" away and the vapour-laden air will (very slowly) exchange with the dry (or, at least, dryer) air outside.

  • 1
    It's worth a try, but considering how murky the trapped water looks, I'm afraid it will leave an ugly residue behind.
    – Elmy
    Mar 6, 2019 at 7:57
  • I too think it would leave a residue
    – Caius Jard
    Apr 5, 2019 at 5:56

My idea is to submerge it in dry rice. The water would be absorbed by the rice.


If you have a conventional (not microwave) oven, you can put it into a pan or onto a cookie sheet and bake the glass cup to drive out the water.

Heat the oven to slightly above water boiling point. The water will boil. The resulting water vapour will leave the cup with the increase of pressure as the vapour expands. (Ideal Gas Law)

As the last of the trapped water is reached, there will probably be some solid residue left trapped within the glass walls. Figure out where you want the residue to accumulate and put that as the lowest point when you position the cup. Bottom down and the residue will end up at the base, etc.

You do not need a very hot oven. You are not in a hurry. It might take up to an hour to get up to temperature. Too fast and you may shatter the cup. A few degrees over boiling will be enough. Keep an eye on the piece and you may locate the source of the opening.

Good luck.


Leaving it in the fridge would dry it out slowly as the air in the fridge is dry! The cooling element takes out all the mositure from the air!

  • 1
    The air in a fridge is damp. Tht's why it frosts up.
    – Chenmunka
    Apr 8, 2020 at 9:02

I place the glass upside down in the microwave and heat it up to evaporate the water - it hasn't cracked on me. But if the water was dirty to begin with you'll still have the residue inside the double walls. The other option, with the glass right side up, suck through the tiny hole to get everything out and spit it out (obviously). It's not the most appealing technique but it works very quickly. You could also try to one of those aspirator bulbs to clean baby's noses.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.