We live in a very hard water place. The unit cost from $600 plus and uses 9 lbs salt per week. That is a hard water hardness of 54 to 60 plus. That gets you just over 550 gallons of soft water. That said, when one states they use a spoon of salt for a week, they are not treating anything. Our unit is 32,000 grains. The tank is about 2 foot tall and 12 inch in diameter. It just fits inside our water section door. The salt container holds about 20 lbs of salt. This was purchase many years ago. The controller head last about 10 years before it needs new parts. If time has past then a new controller is needed at a cost of close to $400 plus. Our home unit is 4 foot tall and runs almost the same in price but just bigger. The salt contain is two foot in diameter and holds Many 50 lbs bags of salt. If you let the salt run out and your are in city water the brine resin will die so to speak. This is due to the fluoride which stop the resin BB from working any more. Cost for new Resin about $120 per recharge. They last about a max of Tens years, depending on your city water Fluoride treatment. Cost to run is 50 lbs of salt per month and water to clean the media. Soft water does not dry you out. Only a table spoon of soap for a load of cloths. Dishes sparkle. Sorry long winded.
http://www.popularmechanics.com/home/interior-projects/how-to/a150/1275126/
The rated capacity of a softener is the maximum number of grains of water hardness the unit can remove prior to regeneration. The hardness of water is measured in grains per gallon (gpg).