I recently purchased a steam iron that requires de-mineralised water.
The instructions say not to use de-ionised water (ie the stuff you put
in car batteries) in the iron but that de-mineralised water can be used
to water houseplants.

You cannot purchase de-mineralised water in the UK, so I have had to buy
a plastic jug and some cartridges of grey granules, (presumably permutit
or similar) through which you pass the water. Here are my questions,
with apologies in advance for their number:

Can someone please explain the difference between de-mineralised water
and de-ionised water?

How does the water become de-mineralised by passing quite quickly
through the granules? (I am told that after several uses, when the grey
granules turn brown, they are ready to discard).

Does it work in the same way as a water softener? The water here is
very hard, so I cannot understand how the same granules can
de-mineralise any type of water.

What benefit, if any, is there to houseplants by using de-mineralised
water?

Many thanks in advance.
--
June Hughes