While I'm a bit late in the game, I want to say I'm very sorry for your losses, I agree that it was probably nothing you did. I know little about newts, but with the ADF's, it is incredibly common to lose them shortly after you get them due to the awful conditions at the stores (crowding, mixed species, poor nutrition, dirty/harmful water, etc), or, before that, the mills. There's some pretty awful videos of what they do to the ones they sell in those frog-o-spheres
.
Also, I think you have very cool setups, I can't wait until I get some aquatic amphibians, I have some nice tanks that are dying to be filled lol.
Also, just as a FYI, they can be occasionally found in regular or specialized shelters or as rehomes, if you are interested in trying to adopt your next ones.
Also, to answer your question about water, you can use distilled, since your water is hard, this site shows the levels of the more common brands and explains a bit:
http://www.caudata.org/cc/articles/Spring_water.shtml