Dyers Pass Road near the Cracroft Reserve reservoirs, 25m drop from there, low pressure had afflicted other homes nearby too. But that matter has been resolved, a few years back.
Change of cylinder from copper, for a solar system installed July 2009, that led to an element failure in 2014 ($230 to replace) then again in July and December 2015. The latter repair changing to an “industrial” Hermetic element ($370 for this).
A sacrificial anode may be tried if the element fails again.
Reading into the technical issue with the Ellwoods, a change of cylinder element (metal) is a lot of the tweak needed in resolving this fault. That is because of the chemical reaction set up inevitably in a weak base water solution drawing metal ions. i.e. Stop the reaction inside the HWC tank by choosing different element metal to leach.
Refs. wikipedia.org/wiki/Hard_water +
Impacts of Water Quality on Residential Water Heating Equipment – U.S. Department of Energy, November 2013 – Pacific Northwest National Laboratory