Hard water (from a well) at the house, and I was wondering what to look for in terms of getting a water-softener, or things to avoid.
For the most part, softeners are pretty simple. Softening water works by exchanging positively charged ions with sodium ions.
Because softeners backwash periodically to recharge, they have a timer (and sometimes a meter) to control when this happens. One of the problems with a mechanical unit is when the power goes out, the time freezes, and just picks up where it left off when the power comes back, so it will start backwashing at strange times - most (if not all, now) electronic timers have battery backup for the time. Electronic ones have been in use for 10+ years now, and are quite reliable now. If you use a metered timer, it will regenerate during the night only after using a certain amount of water, so it wastes less brine (salt) water.
Get one that is easy to service. Although softeners only have to be rebedded about once every 10 years, it should be possible to turn a bypass valve and disconnect the softener. I've seen some old units where you actually have to cut the plumbing to disconnect them, although I'm not sure if those are still on the market anymore. You don't want one of those.
Pay attention to how it is connected: All of your hot water should be soft. Outside taps should be hard (you don't want to water your garden/grass with soft water), with perhaps the exception of a hose in your garage for washing cars. Some people leave their kitchen cold water tap hard, so as to reduce the amount of sodium they are drinking and cooking with, but this partially depends on preference and partially on the amount of hardness (and thus amount of sodium being added). Obviously this is a bigger concern if there are people on low-sodium diets in your house.
Personally, I would avoid electronic/magnetic softeners. There has been some evidence that this can help with very low levels of hardness, there is a LOT of junk out there.
I used to work summers for my dad who ran a water treatment business. We replaced one of these electronic softeners (it had wires going from each end that wrapped around the pipes) with a real softener one time, and took the electronic one back to play with. We tore it apart, and could not find any active electronics in it except for the ones that drove 5 LEDs on the front that flashed back and forth. We hooked the wires up to an oscilloscope and all it was doing was alternating between about +10 mV and -10 mV, with almost no current. I can't see how this possibly did anything -- and the home owner was replacing it with a real softener, so what does that tell you..
Another consideration is the type of salt that the softener is loaded with - some units take 25kg bags, whereas others use much lighter and easier to store salt bricks.
I've worked on software with water conditioning companies all over North America for the past 10 years, so I have a pretty good understanding of the business.
My advice is to talk to several companies in your area about what they recommend. There are tons of dealers out there who can help you. They know the water in your area and the equipment best suited to your needs. Some water requires different filter media. I wouldn't be comfortable just purchasing something on my own, and I do pretty much everything on my own.
I would stay away from plumbers- work with people who specialize in water treatment.
To name a few companies who have dealers who can work with you:
It looks like you're in Boston... unfortunately, I've only worked with one dealer in MA, and they weren't anywhere close to you.
There are several types of regeneration options. Onet thing I would recommend is getting a metered softener rather than a strictly timer option. The metered softener regenerates at a certain time of the day when enough water has passed through it to need regenerated. You will need to have your water tested to determine the hardness and iron levels. These numbers are used to set your meter.
One other thing that was recommended to me was to buy a mechanical metered unit and not an electronic one. The mechanical metered units have worked for years and do not have as many things to fail in them as the electronically metered units.
I bought a softener last year and installed it myself. I got it from the website below. They answered my questions before I ordered it and shipped it to my house for free.