First 12 Cubic meters is free;
the second tier of 31 cubic metres is charged at $4.16 per cubic metre;
the third tier of 19 cubic metres is charged at $6.45 per cubic metre...............
1 cubic meters = 1000 litres.
So your hardworking and daily 20 mins of time (600mins per month) can save you a few cents/ dollars per month. It doesn't make sense at all.