Contaminated Water

[Silversword]

I am doing the Undead City Quest. I need 5 rotten food and 5 contaminated water to give to the innkeeper. I have the food (found in the Undead City), but I only have 4 contaminated water (found 3 in Undead City and one somewhere outside in Freymore). Where can I find 1 more contaminated water?

[Elendil / Redshift]

You can buy it at any inn. The food/drink items at an inn are randomly generated just like any other shop.

There is also a little trick for shopping: save before entering a store (or inn, in this case). If you don't see what you are looking for, reload and try again. (The item generation for the day is done when you enter.)

[DeMenchev]

I believe you can buy it only at the Matras' inn.

[Elendil / Redshift]

Yes, I believe you are right. Only the innkeeper in Matras sells contaminated water (randomly).