Mercury switches in Potable water storage tank?

I've got a 10+ year old water storage tank that just had the well UP switch fail open. As I'm looking at the switch it's a Rhombus Super Single, which is a mercury switch. I'm guessing that all three switches (well, booster and alarm) are mercury. Rhombus says these are not for potable water, and that I should use the mechanical version switch. Is there some reason that a licensed installer would have used the mercury switches in the first place (performance, reliability, never had a leak, etc).

Is there anyone who would say to leave the remaining mercury switches in place, or replace all 3?

Also, if I have to replace all three, should I try and clean out the iron residue in the bottom of the tank, or will this create more problems than it solves?

Thanks for any input.

Bob