Interesting tangent this thread has headed. I always thought the only difference in hot water would be less dissolved oxygen. But corrosion is a big deal in Perth water, I had to replace my last HWS which had corroded out, and the plumber suggested you need to replace the anode every few years in Perth. There are companies that make a business out of doing only that, replacing anodes in hot water systems. So, thinking about it....
The anode is a quite long but small diameter rod, maybe it would weigh 1 kg.
The average water consumption in western society is about 200 l/person/day
I am going to guess about 20% of total consumption is hot water
A house with 2 people in it would use 200*20%*2*365 = about 30,000 l/year
If "a few years" from my plumber = 4 years, the total water through the system = 120,000 l
1 kg of anode dissolved in that water is an average concentration of 8 mg/l
In reality some of that anode metal would probably form non bio-available complexes, and there would be a fair variation depending on how long the water was in the tank, but still, as a ballpark number, thats quite high.
If my anode is zinc, then I wouldnt like to be drinking more than 2 l of my hot water a day.
If my anode is magnesium, then I wouldnt be concerned about that level at all and would drink loads of hot water
Aluminium limits arent very well defined, but I would prefer not to drink much of my hot water at 8 mg/l aluminium.
Might go find out what my anode is made of.