cure for hard water spots?

Your title seems to be asking how to remove hard water spots and your text implies you are looking to understand if a water softener will not cause them with use. There are commercial products which will remove water spots at most boating supply stores. If you shammy after washing you won't have water spots. If you have a spot-zero system on your boat you won't need to shammy- just make sure the boat is waxed and then you rinse with the spot-zero water. Google spot-zero ... it's a water maker which removes nearly all the impurities from water and thus doesn't have any residue which causes spots when the water dries.

The wet spot does in fact work. A residential softener would probably work as well, but not designed as well as something like the wet spot. If you don't backflush either of them periodically with the salt, neither will work after a while. Chamoising the boat dry before the water drops dry will prevent water spots as well.

A water softener is a must for me, not only you don't have the spots , you don't get mineral and scum build up around all the faucets and showers. What you spend on cleaning supplies will pay for a softener. Pressure drop is near zero. Spend a few extra bucks and get one the has a brass control head instead of a plastic one. Also if you shower with water that has 0 grains of hardness you'll never want a shower with hard water again .Most municipal water even if its run through a softener plant is still around 10 to 15 grains of hardness.

I purchased a portable softener/filter this year. It helped keep the water spots off our blue hull (as long as you rinse it after running etc). I bought the stainless water mark unit as the hardware etc seemed more heavy duty than others and apparently a water filter that is not clear is better as light helps "things" grow in the filter.

Max

My experience with these wasn't perfect. They helped s bit but if I wanted completely spot free rinsing, you need deionized water. Google cr spotless, that's just one brand and they are all about the same. There is a cost to the charging resin, and it's bigger than the spotless system mentioned, but they do work.

I'm buying a system for my new boat because the bridge side windows are nearly impossible to reach to dry manually.

As an aside, I costed my old boat and the new one with carpro's CQuartz. It helps repel water very well and lasts, so here is less water drying for spots. The initial coating isn't inexpensive, but I love the results and weekly washing is much quicker.