Quote Originally Posted by GaryP
Also purchase a TDS meter. Without one, an RO/DI can be useless.
I think Bryan's now including TDS meters with some of his filters. But, I disagree that without one the filter is useless. If you buy a decent quality R.O./D.I. filter, you're going to have very low TDS for some time; if you have the D.I. resin that changes color you can easily see when it's time to change that, and after several months of use, you might be able to borrow a meter to make sure your R.O. membrane is still working well. The meters are not expensive, though, so it's not a big deal to get one.