Why the water difference is bigger than the consumption itself

It can look absurd. Two euros on the bill for water used, but six for the difference. There’s an explanation for it, though.

1. Not everyone submits readings. If some apartments don’t submit their readings, their actual consumption ends up in the difference and gets split among everyone else.
2. Readings get taken on different dates. The shared meter is read on the last day of the month. If an apartment’s reading was written down mid-month, a difference appears purely from the math.
3. Readings get estimated “roughly.” A number written down from memory creates a shortfall one month and a surplus the next.
4. Meters have different sensitivity. The shared meter picks up even a thin trickle that an apartment meter doesn’t register. A leaking toilet tank can go completely unnoticed.
5. Leaks in shared pipes. In the basement or the risers, where nobody sees them.

What this means in practice. The lower an apartment’s consumption, the more disproportionate the difference looks. Someone living alone and saving water feels it the most.