Ours is a small to medium size family of 3 adults and 3 small children and we don't waste water. Until mid February this year when we had a maid there was just 2 adults and 2 small children. Water usage through 2011 and April 2012 ranged from 20-30 meter cube (m3) or 145-220 imperial gallons per day which is actually quite high but I took no notice of it. Suddenly from May the water usage shot up to 40 m3 and suspecting faulty water meter which was more than 10 years old I requested for a new meter which was installed in August, i.e. just over a year ago. Sadly the water usage did not reduce, which rule out the meter as the cause. I began looking at other possibilities.
1. The addition of a maid. Usage crept up to the 50s-60s m3. Disciplining her to control water usage didn't bring it down.
2. A new lawn was laid in mid April. Over-watering it in the first 2 months could have explained why the usage went up to 70+ m3 but thereafter we cease watering it daily and none when it rain or shower. Yet in June and July I was hit with a bill of 79 m3, the month before 76 m3. This is getting ridiculous. No way can a family of our size consume 550 gallons of water daily, even if I bath 3 times and wash my car daily and sprinkle the lawn, which I don't.
3. Both water storage tanks didn't leak nor overflow. The water line from the meter into the house run above ground and it is watertight too.
4. The other possibility must be underground leakage, if any.
I did a simple experiment over a week ago. Taking the meter reading one night before we retired, I found the next morning 0.7 m3 water had passed through the water meter while we sleep. So some water must have run out of the tanks that they kept refilling. The next day when I shut the supply to the tanks there was no meter movement during the night. It was obvious that water has flowed out from one of the tank or both tanks. I investigated and discovered while all pipings to the bathrooms and kitchen are accounted for as leak free, there is ONE line that ran underground, under the building from a bathroom, to the tap point on a pillar at the garage. Ah, ha, this must be the culprit. For over a year I've noticed water appearing between the gaps of the floor tiles in the garage and I didn't suspect it to be from underground. Now it is beginning to make sense.
I called my regular plumber who came yesterday to seal off the piping to the pillar tap and re-route the supply from the storage tank to the cistern, wash basin and shower. I was so relieved to have nabbed the trouble maker and look forward to days of reasonable meter readings .... I continue to take meter reading daily for the next week or so to assure myself this water mystery is eventually solved. If not my other guess is THEFT! But how?
Update: Aug 20, 2013
The meter reading continue to spiral even after the bypass operation above. Could there be another leakage? There has to be but where? The plumber was recalled and together we discovered another underground pipe that could be the cause of my woes. It connects the wet kitchen washbasin that receives its water supply from the storage tank above the kitchen roof to the wall tap outside the kitchen. There is a run of some 12 feet PVC pipe between the 2 points under the floor. It never struck me to examine this critically as I wasn't aware of this piping, but after it was discovered on Aug 17 the plumber shuts off the supply from the tank to the washbasin and the wall tap and allow the tank to fill up. Viola! Half hour later when the float valve shuts off the inflow the water meter stopped running. It was a magical moment at which I literarily jump with joy. We finally caught the water guzzling monster!
The 24 hours after that saw the water consumption dropped to just 0.7 m3 and the next 24 hours confirmed this usage. The plumber came today and pulled a new set of piping from the tank to the washbasin, wall tap, washing machine and the bathroom. The meter now runs only when there is water usage. I'm really glad the water mystery is exposed. Case closed.