Rotten/spoiled water

I’m having trouble finding rotten water to deliver to the undead city. I can find sometimes rotten foods, so that is not a problem, but finding rotten water seems really hard. Where is a good source for rotten water? Someone said to try inns, but they just sell the normal healthy foods.

Maybe try the inn at Matras, they sell cheap items.

Found them all after adventuring back and forth all over the global map. Took quite a long time, but … then I found a cache much nearer after the quest was completed