Travelover,
I'm on a well also, with very hard water (34 grains/gal). I installed a water softener to reduce the hardness for all the water in the house (except an outside house bib). My drinking water goes through two sediment filters (30 micron and 5 micron), and the RO canister. Then, through a small "finishing filter" of activated charcoal. Final step: a small UV light that kills any bugs. This drinking water system is plumbed to a separate tap at our kitchen sink and to the icemaker in the freezer.
As you probably know, your water softener adds sodium (or potassium, if you use a salt substitute) at a rate proportional to your original water hardness. So, if you have really hard well water, your drinking water will end up with a lot of salt in it unless you remove it. The only practical ways to remove it are with an RO system or by distillation.
Distillation: Unless you want to mass with a "batch" system that makes a gallon or two at a time, distillation equipment is pricey. Also, the electric costs over time are considerable. And, there's maintenance of the equipment . I wanted the convenience of a tap at my sink and a functioning icemaker, so I went with RO.
Back to your original question: I've read that the RO membrane needs to be replaced every 2-3 years, but like you I don't know how you'd tell if it wasn't working. I figure one of two things might happen: either the water volume will decrease (i.e. clogged up membrane) or the water quality will decline (i.e. membrane degradation). I can see if the water quantity has declined, so I'm not worried about that. For about 20 bucks you can get an electronic tester that tells you the amount of dissolved solids in your water (they even make sink taps with this gizmo built in). If your RO membrane goes bad, your dissolved solids would go up (since the salt from your water softener would get through) and you'd know to change your RO membrane. If this testing allows you to get another year out of your membrane, then it has paid for itself.
Other notes:
- If you get an RO unit, consider getting a "permeate pump" too. It costs about $100 more (IIRC), but it will dramatically reduce the water waste of an RO unit, especially if your water pressure isn't high to start with. Remember, even f you are on a well, you pay for electricity to pump that water and getting rid of it costs money if you are on city sewer or loads up your septic system.
- The UV light unit costs about $30 for a replacement bulb I'm going to cut that cost by 75% by fabricating my own holder next year) plus a few buck in electricity. It kills just about every type of bacteria or virus. We had some coliform bacteria in the well when we moved in, and I knocked it out with bleach. Still, I didn't want to worry about it anymore, ad this has been cheap insurance.
- I'd recommend you get a comprehensive water test if you haven't already. There's nasty stuff in some places, and when you have a well the entire responsibility for dealing with it is on you.
I did all my installation myself, and the drinking water system (3 filter cannisters (2x sediment plus the ability to fit a charcoal filter later), RO membrane with pressure tank, permeate pump, polishing filter, UV light) ended up costing me $340 (in Jul 2005).
samclem