How does a water softener work?
A water softener removes calcium and magnesium from your water supply and replaces them with sodium. Hard water comes in, soft water goes out.
Hard water enters a mineral tank from your home's main water source, passing through plastic beads that, through the magic of chemistry, attract minerals like calcium and magnesium, pulling them from the water. The minerals stick to the beads and the water passes to the brine tank.
The brine tank contains sodium or potassium. Ions of sodium or potassium stick to the water, replacing the calcium and magnesium ions the mineral tank pulled out. This process is a called an ion exchange.
Those plastic beads in the brine tank get covered in calcium and magnesium, so they need a periodic rinse. The control valve determines when it's time to rinse the beads. Most new water softeners have a computer to sense when to clean the beads, based on your water usage. In a family household, the beads usually get rinsed every couple of days. The cleansing process is called regeneration.
What types of water softeners are there?
There are four different types of whole-house water softeners, each of which come in a different price range.
Ion exchangers
Ion exchange water softeners cost $400-$1,000 for a basic unit. Also known as a conventional water softener or a salt-based water softener, they're the most common type of system. They work like we described above, and usually use salt as the exchange medium.
Salt-free
As the name implies, a salt-free water softener (technically a conditioner, not a softener) use a medium other than salt – usually potassium – to make soft water. Potassium is safer for septic tanks, which can corrode over time if you use a salt-based softener. People on low-sodium diets prefer salt-free softeners, too.
Salt-free water softeners work a little differently than salt-based ones. Instead of removing calcium and magnesium, a non-salt softener suspends them in the water so the minerals don't build up in your plumbing. Those suspended minerals will end up in your water heater's tank, though, where they can damage the tank. Dual tank
Dual tank water softeners have two mineral tanks and can soften larger quantities of water, so they're a good choice for large families who use a lot of water. Two tanks means there's no down time while the control valve is cleaning those plastic beads, so you always have access to a softened water supply.
Magnetic/electronic
Magnetic water softeners, or electronic, are a controversial and fairly new type of water softening system. It's an electric device that attaches to your pipes and creates a magnetic field to reverse charge mineral ions as they flow through the pipes, which its manufacturers say prevents mineral build-up in plumbing. While many homeowners swear by them, some water-testing associations say magnetic water softeners don't work.
Water softener size
Water softeners are measured by their capacity and the larger the capacity, the more it will cost. Water softener capacity is measured by how many grains of calcium it can remove from water per day. For most homes, a 32,000 grain unit is enough capacity, but you can get water softeners as large as 110,000 grain.
The water softener capacity you need will depend on how much water you use on a daily basis. If you have more than five people in your household, you'll need a larger water softening system. Because more people use more water, and more water usage means you'll need a more powerful water softener system.
The size of your home can also impact the size of the water softener you need. If your home is larger than 4,000-square feet, you'll need to get a 48,000 grain or larger water softener.