1546pln for 5 months
Well, that`s a lot. But anything is possible. Why don`t you check the water meter? They are in each apartment and house in Poland. Did you write down the meter reading for used water when you moved in? How much have you used since then? Phone the building administration to ask for the price of water.
Is your toilet OK? Doesn`t it leak water? Such a situation happened to one of my lodgers in the past - she ignored the problem for a few months, didn`t notify me about the leaking water tank and finally had to pay 2.500 more for wasted water.
A typical water meter: