Over the last week I have noticed a strange sound of running water (like a tropical fish tank) from behind my instrument panel/ steering column. It's more prominent when in drive or reverse and with my foot firmly on the brake and stationary. I have also experienced loss of brake assistance once in this last week whilst pulling off my drive. Checked brake fluid levels and all seems ok.
Has anyone ever experienced this noise/ brake fault?
Is the noise and the brake failing connected?
Please let me know your thoughts.

Did your brake pedal go hard ? sounds like your leaking air from the brake servo which will require a replacement brake servo unit. 2006 4.2 Supercharged Buckingham blue
2003 BMW X5 4.6is Estoril blue
2006 Yamaha FZ6

No, when the brakes seemed to fail there was longer movement on the foot pedal with very little resistance. I was only pulling off my driveway so not travelling at speed (thank goodness) but it felt like trying to stop the car without having brake pads fitted. Quite a lot of effort was required for very little brake effectiveness.
Since then (plus once when my wife experienced it on the same day), the brakes have felt fine but I'm reluctant to use it. The water noise is still there and the last time turning off the ignition it sounded like lots of water draining back to a tank.

I may be completely off beam here but i get this when starting off when cold and the FBH is running. It is not very loud but I assumed for some reason I was hearing the diesel from the FBH pump moving in the pipe.

Sounds like oil in the brake servo causing the brake issue. There's a recall for some earlier models that resulted in a new oil separator and reworked vacuum piping. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Agree it sounds like the brake servo and vacuum system recall may not have been done.
Regards
Barry 2017 Range Rover Sport TDV6 L494 SE Fuji White
2011 Range Rover Sport SDV6 L320 SE Fuji White Loved but GONE
2010 TRAKKA Motorhome Fiat Ducato GONE (What a dud, don't buy one)
2006 Discovery 3 SE TDV6 Automatic Chawton White/Ebony. Loved but GONE
2006 BMW X5 diesel White/Charcoal, Bought new, Gone after 12 years! Was Excellent.
Ex Member Range Rover Club NSW

The vehicle is a 56 Plate tdv6. How would I know if the recall has been done or not?
Is their a recall code?

Call Land Rover customer services and have your VIN to hand. They have records of recall work but not general servicing for vehicles of our era. 2008 MY Java Black TDV8 HSE

I shall give them a call in the morning and see what happens.
Any further advice is welcome, thanks.
Does anyone know the year this brake servo & vacuum system recall happened?

it was done on both my 05 and 06 silverRRS 2.7 TDV6 22"WHEELS FULL COLOUR CODE,STEPS,REMAP..gone
Rimini red rrs 2.7 tdv6 steps. Full c code. Recon engine!!loved but!gone ,thank god !!
Gone rr sport supercharged. Loved but 11mpg !!!
current,triumph stag mk2...current bmw 325 sport convertible

These are the vehicles affected,

Vehicles produced between November 2005 and April 2007 (Discovery 3 vehicles LA367110-LA440000 and Range Rover Sport LS929086-LS117000).

Vehicles produced between May 2007 and June 2009 (Discovery 3 vehicles LA440001-LA513325 and Range Rover Sport vehicles LS117001-LS215618).

Recall number is I think PRA 2010/11848

Regards
Barry 2017 Range Rover Sport TDV6 L494 SE Fuji White
2011 Range Rover Sport SDV6 L320 SE Fuji White Loved but GONE
2010 TRAKKA Motorhome Fiat Ducato GONE (What a dud, don't buy one)
2006 Discovery 3 SE TDV6 Automatic Chawton White/Ebony. Loved but GONE
2006 BMW X5 diesel White/Charcoal, Bought new, Gone after 12 years! Was Excellent.
Ex Member Range Rover Club NSW

My VIN number does not match any of those numbers. What are those numbers listed?

That's the list of VINS off the recall in Australia and I presume that the range would be the same for UK or Oz.
I had to have it done on my 2006 D3 now gone.
Sounds like its not the issue then.
Regards
Barry 2017 Range Rover Sport TDV6 L494 SE Fuji White
2011 Range Rover Sport SDV6 L320 SE Fuji White Loved but GONE
2010 TRAKKA Motorhome Fiat Ducato GONE (What a dud, don't buy one)
2006 Discovery 3 SE TDV6 Automatic Chawton White/Ebony. Loved but GONE
2006 BMW X5 diesel White/Charcoal, Bought new, Gone after 12 years! Was Excellent.
Ex Member Range Rover Club NSW

It does sound like oil in the servo. Ignore the recall vin range and push LR to replace Free of charge. Safety issue.
Sounds like you'll need a new servo, possibly master cylinder and vacuum hose. Bodsys Brake Bible
Software Updates Contact me
RRS Timed Heat/Remote kits - Contact me
BAS Engine Re-maps/ EGR Blank EuIII and EuIV
Clock On The Dash/ SNOTM /3Flash / BT Update /Service Reset/Error Codes read\ Gearbox Reset
See it HERE

Free of charge. Would that be possible on a vehicle of this age (56 Plate)?