I’m sure you’ve seen one of these:

And you may have wondered why they’re so expensive. And possibly why they need to be replaced in the first place. I can’t really answer those questions, but I can show you how to save money on replacing them.

You’ll need the following tools:

• Water filter
• Exacto-knife
• plastic or rubber stopper
• funnel

Using the exacto-knife, cut around the perforated hole in the center of the top. When you’re finished, it should look something like this:

You’ll also need some activated carbon, preferably a small grain. It is sold in aquarium stores (for water filtration) as well as most home improvement stores and home-brewing stores. This is not the only active ingredient in the commercially available filters, but it does most of the work. If you know where to find ion-exchange resin, email me.

Now, put the funnel in the filter and fill until the filter is about half full.

Then you can cork it and you’re ready for action!