Why Bother, Its just an RV?
So yes it is just an RV, but it is still you, your clothes, your hair, your dishes and so on. Soft water means less soap, less residue to clean up and generally speaking a cleaner RV inside and less maintenance of soap scum, mineral build up and so on.
Most units sold on the market today are anywhere from 8,000 to 20,000 grain units, which are meant to connect on the garden hose just outside of your rig. That is the way most people use them, and there is nothing wrong with that, if you don’t mind cooking with softened water and having it run to everything in the rig, toilet and all. Keeping in mind having it connected that way keeps everything cleaner is nice, but it also means that your actual lifetime between recharge cycles will be fairly short. As full timers and just the two of us, doing our laundry at home and having a 10,000 grain unit, it usually needs to be recharged about every two weeks.
Considering the fact that it takes about 30 minutes to do the recharge and only 2 containers of standard table salt, its really a good deal. You do need to back flush the softener about every 6 months, which will add about 30 to 45 minutes to the normal routine and requires inverting the water flow through the unit which can be a pain if you don’t have all the right fittings on hand.
Now if you are a real fanatic about things and you can plumb your unit into your rig in such a way as to conserve on where the soft water goes, you could do what is done in a sticks and bricks home and separate the kitchen sink, and toilets from the rest of the cold water coming from the softener. In the right kind of rig that might be doable with a lot of re-plumbing and time. It may also be more reasonable to consider a little re-plumbing, and having just the Hot water connected to the softener. Connecting just the hot water would still require a bit of internal plumbing changes, but it would greatly extend the length of time you have soft water for reasons of cleaning etc, where you are mixing hot and cold, or maybe using only hot water.
Advantages to not having soft water on the cold side, is you won’t be wasting the treated water and you won’t have salty water in your cooking or coffee. But you will loose the reduction of mineral deposits that hard water can leave behind.
So its your call, treat more often, have soft water everywhere, even minute amounts in your coffee, or treat less often and clean more! the other aspect is hiring someone like me to plumb it in the right way, separating the cold water systems, like your Kitchen sink and refrigerator and toilets from the soft water system, giving you the best of both worlds. soft where its needed and wanted and reducing the maintenance cycles of the softener.