We purchased a 1966 built condo recently and got a Culligan softener and RO system installed due to the extremely hard water in Morristown NJ. The Culligan system is all PEX pipes and our existing pipes are copper.
This is a co-op condo where the HOA supplies hot water through their boiler in...
Back in mid-2009 dunbar plumbing (known as roast duck at that time) posted some pics of a water heater with out of plumb heater connections at the top. I believe the cause of the failure was water hammer.
Read here: http://www.hotwater.com/bulletin/bulletin11.pdf