Miss Perspicacia Tick wrote:
[...]
You're now probably thinking "where can I find distilled or
deionised
water?" Can't help you there (someone else might be able to
though).[...]

Halford's etc. Melting clean frost from a freezer should do, too.

But I don't really hold with soil testing for ordinary amateur
gardening: the plants usually tell you all you need to know, and
perhaps more reliably.

--
Mike.