From what EV607797 has in the original post, the off-peak power is for the whole installation, not just hot water-is this correct?
From what I was told, it consists of a single meter in a typical all-electric residence in Canada. Basically, the metering is all or nothing.
We tried the separate meter plan in the US for the water heater, citing that hot water was a necessity while heat was a luxury back in the 1950's and 60's. I don't know if that was a government thing or just a POCO idea. Virginia and North Carolina are full of older services where a separate meter socket was provided for the water heater. All of those installations that I have seen are bypassed now and have blank covers in place of the second meter. The only signs of that logic nowadays are remote control devices on water heaters that were installed in the 1980's. Honestly, I am not sure that these programs are still in place. I can tell you that many of these remote control units fail and we have to bypass them to restore service to the water heater. Nobody ever says a word.