The brief
The Touran had been needing coolant replenished between regular service intervals, the level creeping down with no obvious puddle. A recurring top-up like that signals a coolant leak, and an engine that runs low on coolant overheats, which can warp a head, so he brought it in before it got there. Coolant doesn't go anywhere on its own. When the level keeps dropping, something is weeping it out, often slowly enough that it evaporates before it pools, and on these the water pump's shaft seal is a common source, weeping a little every time the engine runs. Catching it early means a tidy job; leaving it risks an overheat.
The diagnosis
A pressure check traced the leak to the coolant pump's shaft seal, weeping a little every drive, with the hoses, the radiator, the thermostat and the expansion tank all checking out clean. That's a pump replacement, with a fresh seal, rather than chasing a slow loss around the system or topping it up onto a leak.
The work
The cooling system was drained, the drive belt section released, and the failed coolant pump removed. A new genuine VW-spec pump went on with a fresh seal, the belt set back up, and the system refilled with the correct coolant, the air bled out the proper way, and held under pressure to confirm the seals were dry. A road test confirmed the level held and there was nothing weeping.
The outcome
No more top-ups needed, the level holding, the gauge steady, and the leak fixed. The Touran went home with the cooling system back to spec. A weeping coolant pump only gets worse, and the failure at the end is an overheat that can cost a head gasket, so catching it on the recurring top-up kept it to a straightforward job.