WODA
S

It is likely that the letter S indicates STAROGARD - the old city, it is not clear whether the lid belongs to this city, the old part of Warsaw or perhaps the location of the lid manufacturer - the same is true of another very similar lid Click for cover's details

Photographer’s Note: While the etymology of "starogard" is clearly understood by everyone in Poland as "the old city" or similar...
... no-one would use it towards the the Warsaw Old Town or any historic old town for that matter.
The most natural explanation is that the foundry was/is located in the city called Starogard.

WODA - water