My td5 ( 2001) has been using significant amounts of water. No obvious leaks. But constant driving would require frequent stops to allow for cooling and then 3 or 4 litre water refill. The gauge isn’t rising above the half way mark at any of these moments and will usually rest at the below half mark for the duration after warming up. I’ve put new recommended concentrated type coolant in, but seemingly to no avail. After 15 to 20 minutes of driving I can be sure there’s been a loss of around a litre of contents, I replaced an old top hose set up with a new one thinking I noted some loss of integrity around the hose layers. So in sum, no leaking signs, new hose, coolant added, but water disappears. Any thoughts or advice welcomed as per.

wots the oil level like?

Can you see any leaks ? the expansion caps are known to fail over time and allow coolant to pass out of the overpressure pipe. easy way to check tape an old water / coke bottle over the pipe and see if it fills up.

another good place is the rubber joining pipe under the turbo.

But that much leakage is not good.

Cheers

Landy temp gauges are rubbish so don't put too much reliance on the readings. May be worth going to a local garage for a sniff test to see if head gasket is leaking

And check the oil level to make sure the water’s not going into the sump!