Questions & Answers about W upalny dzień piję więcej wody.
What case is upalny dzień, and why is it used after w here?
Here upalny dzień is in the accusative singular. Although w often takes the locative when it means location, Polish also uses w + accusative in some time expressions, such as w ten dzień, w każdy piątek, and w upalny dzień.
So w upalny dzień means on a hot day.
Also, dzień is a masculine inanimate noun, so its accusative singular looks the same as its nominative singular. That is why you see dzień, not an obviously different form. The adjective matches it, so upalny also stays the same.
You may also see w upalnym dniu, but that sounds more formal or literary here.
Why is it więcej wody, not więcej wodę?