[Shop-talk] Water de-ionizing resin?

[Obaa]

Somewhat on topic, maybe?

I got a water de-ionizer last year as a present; it's this one:
http://www.costco.com/Browse/Product.aspx?Prodid=11201522&whse=BC&topnav=&browse=&lang=en-US

The thing works really well if I limit the water flow through it to a level it can handle; I can wash the car on a hot afternoon and not worry about drying it off.
It's seen enough use now that the resin for de-ionizing needs replacement (there is a meter built into the device which monitors water quality).  The only source of this stuff that I am aware of is from the manufacturer, who thinks quite highly of it based on the price.  I'm sure this stuff must be generic across different companies, but I'm not sure what it is, or how to look for it.  Do any of you know what an equivalent substitute and source might be?

Thanks!