I live in Phoenix and my dishwasher stopped working. I found out all
of the washer heads were plugged with white flakey stuff. I pulled it
apart and the thing was just filled with deposits. I assume this is
due to our very hard water. I am now considering a water softener.

But then I hear that you don't want soft water for your plants, and I
have a automatic irrigation system around my house. I also have a
swimming pool with auto-filling system -- is soft water good or bad for
a swimming pool (just for topping it off with water due to
evaporation)? In reality hard water is bad as eventually the pool
water gets so hard that you have to drain it. Would soft water fix
this and indeed be a good thing? I have a salt system for my pool
which means I believe it has dissolved sodium in it anyways, so maybe
it doesn't matter.

In any case, on to my real question. I am considering soft water
primarily to protect my appliances, showers, bathtub, etc. Would it
make any sense to just install the soft water system before my hot
water heater? This would protect my hot water heater, dishwasher,
washing machine, and we'd have mostly soft water for showers/baths.

Also, is it possible that my hot water heater is filled with this stuff
as well, making my problem worse? My house is 7 years old, never had
soft water.

Thanks!