Usually you can get 10 years or more on city water and 5-10 years on well water that has iron, manganese or high levels of organic contamination.
The things that make the resin fail sooner are coating or oxidation of the resin.
Iron, Manganese and Organic contamination will coat the resin making it ineffective because they interrupt the ability of the charge to hold and let go as needed. An automatic resin cleaner
can greatly increase the life of resin that is subject to fouling.
Oxidizers like Chlorine and Ozone attack the binders in the resin and turn them into fragments. Some of these fragments then get washed down the drain during regeneration causing loss of resin and capacity. With high levels of oxidizers the resin may turn to a jelly consistency. You can extend the life in this case by pretreating with activated carbon
Common question from clients.
We have a 12 year old water softener but recently the water doesn’t seem treated so well. I had a sample tested today that came back with 17 grain and the village water is known to be around 26. So there was some improvement but not a lot.
The system seems to cycle fine and consumes salt at the usual rate it always has. Just wondering if the resin might have worn out (can it wear out or is it inert?).
Yes it sounds like you have a problem. Usually you get 5-10 years, but it really depends on the water. You could have a problem in the head that is letting hardness pass through the head. If it draws salt, that is good, but you could have a bad bypass valve or some other problem in the head.
So here are some options
Change the resin - see Selecting Resin
and Changing Resin
You could change the head and the resin see Control Valves
Or you could just replace the softener and be trouble free for another 10 years.
See Selecting a softener
and Water Softener Calculator
Also a general article about water hardness and solution can be found here