Hi.  Everytime I open the filler cap there is quite often a little puddle of water.  And lately seems like diesel.  Why is this ??

Edited November 2, 20232 yr by Robere

Thanks Robert and welcome.

When you say ‘open the filler cap’ do you really mean fuel cap, or fuel flap? 
Kind regards,

Gareth. 

Fuel flap.  As you open it where you put fuel in where nozzle goes just below inside door water or even diesel lies 

That sounds much clearer Robert, and now makes sense. 
If you open the flap as normal and without removing the cap, thoroughly clean around the cap area and all inside the area that the flap conceals. 
You should then see a small rubber grommet or similar, in the bottom of the cleaned area - usually directly below the filler cap -i.e. at the lowest point of the compartment. You should then see a small (3mm or so) hole in the centre of the grommet which ( when clear - important) allows rainwater to run away. Get a length of suitable flexible wire and push that through to clear the blockage - which is likely to be further down.

Diesel sometimes? Dribbles of diesel out of the fuel hose when returning the hose to the pump. 
Let us know how you get on.

Kind regards,

Gareth. 

Perfect all sorted thanks for sound advise

Is the little hole below the filler neck blocked? It's a hole that's supposed to be a drain.