John Laird wrote:
I have a modest amount of standing water in the sub-floor of my humble
abode, which I would like to get rid of before I go crawling about,
endeavouring to find where it has got in. Having wasted lots of time
with Google, I've not really found any simple, inexpensive, pumps that
would do the job, so does anyone have any clever ideas ?

The water is maybe 1" deep at its worst, and as far as I can tell,
most submersible pumps will struggle to get down to half that before
cutting out. I found a "puddle-sucker" on one or two sites, which
will go down to a few mm, but at a price. (£100+)

I expect I will end up using my Vax wet'n'dry cleaner, carefully ;-)
It won't care about a bit of grit or the odd small stone, as long as I
avoid letting it overflow...

Once the floor is dry, I thought I might scatter some tell-tale powder
around in order to track the water origin (assuming it's not coming
up, which seems unlikely). Again, any advice much appreciated.

TIA.

If the surface of your subfloor is below the water line outside (water
table) then you won't be able to drain it properly...what you can do is dig
a sump hole about a foot wide and deep and have a submersible pump running
in this via a float switch, or you could build a soakaway...either way,
atempting to fill cracks etc is a waste of time and effort.

It could be a leaking pipe, have you never noticed it before?