In message , Janet Baraclough
writes

The easiest cheapest way to save your steam iron or houseplants
from hard water minerals, is to use rainwater. Failing that, if you have
an old-fashioned freezer that requires periodic defrosting, bottle some
melted ice. Both waters have previously evaporated then condensed again,
which means they don't contain any appreciable amount of groundwater
minerals.

Unfortunately, my freezer has no ice and the outside water is channelled
on to the garden, although I could redirect it to a container for
houseplants. I still can't understand how a few seconds filtering
through the grey granules de-mineralises water.
--
June Hughes