If you need it for rinse, build a small RO, 100-1000 gpd are readily available to build on your own.
If you want it for the pump feed, REMEMBER, that softened water lack some minerals and makes bad companion to brass and some other metals.
Give me a call, and I can steer you with the leads for a home made system for water softening.
As well, I think that Jerry at Sirocco, build some stoner systems. 800-400-CLEAN