I have found that as of late our water kefir concoctions have not been used as much. My daughter was the only one who wanted some. Pregnancy made the taste and smell suddenly unpalatable and my husband was working 12-16 hour shifts and not gone to drink it. I decided instead of stressing out and starving the grains by accident through forgetfulness and underuse that I would store them until a time they could be used more. I decided to freeze them.
To freeze your water kefir grains (milk kefir grains need an additive before freezing so this is specifically just for water kefir grains) you will first need to dry your grains. I added a piece of fruit to my jar the day prior to color the grains a bit. They are essentially clear so they can be potentially overlooked if you drop any. First you will need a fine strainer to clear off the liquid. I use a plastic strainer as some suggest using metal can have adverse effects on the grains in time. The plastic is also easy to poke and manipulate if any of the grains decide to stick.
Then use a paper towel to let them sit and dry for 2-3 hours at least. You can pat them down slightly if you wish. We generally use crocheted dish cloths and store bought cloths in our home but this made it easier to see the tiny grains.
Place in a jar when dried (they will still be gelatinous but fluffier). Close with a tight lid and place in the freezer. I stuck mine all the way in the back. A deep freezer would be even better. These should last at least 2 months in a regular freezer that is opened a few times a day. Longer can be attempted but it seems the longer they are frozen the more of a chance they have to not do great when defrosted.