"June Hughes" wrote in message
...
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:

Deionising cartridges contain deionising resins.
If I remember rightly, Permutit is not a deioniser proper, but
replaces positive ions by Sodium ions. It is esentially only a water
softener.
I suspect that what your instructions mean is that you should use
permutit to soften the water, because it is the Calcium and Magnesium
ions found in hard water which make scaly deposits which are replaced
by Permutit.


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

Deionising means replacing all positively and negatively charged ions
by the H and OH ions of water itself.
Deionising produces the purest possible water--- even purer than
distilled water. It is a relatively expensive process to deionise
water.
Demineralising in the present context sounds to me like softening the
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).

The deionising and softening resin granules are pretty hungry for ions
and work fast.
When the deionising resin changes colour, it is ready to be discarded.
Permutit, on the other hand, can be recharged by soaking it in a
concentrated solution of kitchen salt.

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.

See above

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

Almost none, except if you have lime-hating plants.

Franz