If we look at the bills correctly on certain months it is
estimated reading for water and electricity and gas etc. The SP
guys can't be reading the meter every month for every HDB household
rite? It will work them to death ! 
So usually those estimated readings for the month will be moderated
the next month when actual reading is taken. That is I found out
after 1 yr and observing the pattern usage on my bill. So to
determine more accurately is to take the average over 3 months bill
which I presume within that 3 month a meter reading is taken.
For me, 2 person water,electricity,gas is abt $60 - $70. The
conservancy charge is $60.50 every month fixed.
A side note: toilet bowl for urine and shitting is termed as water
fitting and cost $3 each per month regardless if you got use. So
ppl with 2 toilets at home please alternate to shit and urine on
both of them
