The Fat (2011 4.4TDV8) one is using water, it’s been pressure tested and can not find any leaks, I cannot smell any coolant, and there’s nothing inthe oil. Any thoughts.? 2011 TDV8 | overfinch genuine build | mapped

There is a leak somewhere.

Engines do not consume coolant unless it is leaking out of the cooling circuit, or being burned via cylinder entry.

Once correctly set, the coolant level should never change. 2012 (L322) 4.4TDV8 Vogue SE, RSE, Fuji White over Arabica.
Previous V8s: BMW 645Ci, P38 4.6, P38 4.0, Merc CL500
Previous others: Honda x1, Volvo x7, Rover x6, BMW x6, Ford x1, Mercedes x2, Skoda x3, VW x2, Renault x2, Citroen x1, Mazda x3, Nissan x1, Audi x3, Kia x1, Fiat x4, Subaru x3, Austin x2, Triumph x2, Jeep x2, Hyundai x2, Lexus x1, Mitsubishi x1, Saab x2... and some others I've forgotten!

https://www.fullfatrr.com/forum/topic66813.html

Just a tip from reading the link Mr Dolphin posted.

Having just done some coolant hoses on my car, I did not realise that when you reconnect them you should have the little metal clip in the closed position before you push the hose on. You will know when its home properly as there will be a good audible snap.

I was trying to push the hose on with the clip "out" and the push the clip down, but that is not the correct way

Firstly, any engine not 'using' coolant between services is very rare - especially with a compacted Graphite/Iron block as used on most PSA engines. It's not uncommon to top-up the coolant level <1 litre at service, whatever marque it's from.
To the question:-
If there are no external leaks, then clearly it has to be internal - EGR cooler or transmission cooler are both good places to start - neither would necessarily show up with a pressure test.
Is it actually losing coolant or is the coolant level warning suggesting it is? I'd also have the system pressure checked when hot as that can show up issues not apparent on a cold engine.
Is there steam/smoke from the exhaust a few minutes after starting or after a run?
Has the coolant pressure cap been tested?

I have a leaking EGR cooler. It uses about 1L every 2-3k miles and the rate has been constant for 2 years. The cost of replacing the EGR cooler is very expensive as it's a pig of a job to get to so am happy to just keep topping it up. 2012 TDV8 Vogue (L322)

+1 for the EGR cooler. Known weak point.

Check the radiator hoses attached to the front of the thermostat housing. The top one of mine was leaking a little so I replaced the seal with an o-ring 45mm x 3.5mm in Viton 75. The top hose moves with the engine so wears the seal whereas the lower hose doesn't move because it is restrained so its seal hasn't worn.

Slow coolant leaks come of age and mileage.

You can block test quite easily with a head gasket test kit (although this is very unlikely on a 4.4 TDV8), but will give piece of mind.

If the leak is only minor, personally I'd recognise the age and mileage of the vehicle and just top it up as required, for example when you clean the MAP sensor, if it needs tending to every 1,000, or at oil service if it only needs every 5,000-7,500. 2015 Range Rover Autobiography 4.4 SDV8