Fyi, a fellow by the name of Jim Schulman wrote this: [Water FAQ] (https://web.archive.org/web/20080526072324/http://www.big-rick.com/coffee/waterfaq.html)
from which I extracted this long piece of text (sorry!):
Obviously, no one in their right minds would want to go through the hassle of doing a boiler descaling at monthly or bimonthly intervals. Fortunately, one can reduce the descaling requirement to virtually nothing, even when running the 90 mg/l hardness, 50 mg/l alkalinity water best for coffee by using this trick.
If the boiler autofill only runs to replenish water lost by steaming, it only amounts to a few ounces per day. Suppose the water in the boiler starts out very soft. Then these small additions of moderately hard water won’t bring it to scaling levels for at least a week or so.
So once a week, put very soft water into your tank and flush the boiler with it until the water has been softened down. The flushing technique is the same as that described in the descaling section. Then put your regular nuetral to moderately hard espresso water back in and enjoy your shots with complete confidence. If you regularly use boiler water for Americanos, etc., or do a lot of steaming, adjust the frequency of soft water flushing to match [see section 1.7]. If this is impossible due to very high use or boiler inaccessability, you will have to go with a softer non-scaling water.
Straight RO can be used for this flushing since enough minerals will generally remain to operate the autofill sensor. If the pump doesn’t go off due to low minerals, simply shut the machine and replace the RO water with the regular water. It will only take a few seconds of pumping to raise the mineral content enough to deactivate the autofill. Alternatively, add 5% to 10% tap water to make it conductive enough.
Even if boiler safe water is used, the boiler needs to be flushed occasionally. The frequency can be calculated using the data in section 1.
If these procedures are followed, there’s technically no need to descale the boiler at all. Nevertheless, an annual or biannual descaling is wise to pick up any stray scale that may have formed due to forgetfullness._