What is the life of the filter if it sits unused from one summer to the next?Thanks.Dan

I still have a First Need filter line this I bought 25 years ago. It sees sporadic use, but I just used it on a weekend hike and it worked great. As the previous post mentions wear and tear is based on usage. You can extend usage by back flushing after every use when you return home with a mild bleach solution. I also recommend using a pre-filter that you can put on on the end of the pick up hose. It will filter out the larger debris and particles.

I know we let mine sit for probably 2 years after using it for 1 trip and it no longer worked.

The life of this cartridge is based more on usage rather than time or shelf life. If it remains unused, theoretically it could last as long as the materials remain intact which could be decades.