dfk41 Does your RO machine remineralise the water? Only those with a DI resin filter (rather than a remin/alkaline filter) take all the minerals out.
Remineralised RO water can be harder than Ashbeck, Cornish & water from Glasgow. Pretty sure you’re allowed to use the Moccamaster in these places.
If in doubt you could mix 50:50 tap & RO until you can check the KH/alkalinity of your water mix.