By chance I lifted the boot floor cover over the spare wheel to find at least 50mm of water filling the well!  It must have been there for a while as some steel parts had started to rust.  Any idea how it could get there?  None of the rest of the boot is wet or stained.

Hi David.....welcome to the Forum

Haven't come across this before but I wonder if one of the rear lamp units has been removed before and put back in correctly?

This is usually a good place for water to leak through into the boot

Let us know what you find

David in Devon asked about water ponding in spare wheel well.  I had same problem in my 2007 CRV, which I eventually found to be water coming in along back wall of well, where original sealant is smeared.  Sprinkle talcum powder onto the vertical face and inspect for 'runs' in the powder after rain.  I applied auto sealant from the inside to seal the place(s) of water ingress.  It seems to be OK now, 4 months later.   ps:  I drilled a small hole, approx 2mm Dia, in the middle of the well to drain any water, but careful where you drill the hole!