Plenty of results of internet searches about this seemingly common problem. Took off a plug lead and one side of the plug chamber had half a thimblefull of water in it. Plugs had tracking marks, diagnostic said misfire cylinder 1. Cleaned all out, cleaned leads, replaced plugs. A few weeks later, the fault is back, this time the water in the other chamber.

Checked carefully around washer jets with watering can, no leaks, although water does appear to travel from around the wiper pivot and into the engine bay over the exhaust manifold, not sure if a gasket or rubber washer might have gone there - is water supposed to drain around the wiper shaft?

No fault code showing but car running badly so about to try new plugs and replacement leads but not sure how trace this water leak. Not convinced its a core plug as it changed sides and there is no loss of coolant, car well maintained etc.

Any advice from the Backroom boys?