install a new main shutoff and a new meter.
if there is a buried pipe from an outdoor meter to the house, replace
it.
stop putting bleach dispensers in the toilet tank.
replace all toilet tank fill valves and flusher fixer.
see:
http://www.fluidmaster.com/
some briefly quoted he
" Leaky toilets waste more water than you think. Silent trickle or
constant flow, every leak is a costly one.
Leaks caused by old toilet parts waste water, bloat your water bills
and cab trigger serious water damage.
It's cheaper to fix leaks than pay for them. The sooner you detect and
replace faulty tank parts, the faster you'll save water and money.
Fluidmaster parts and kits make the job easy. Read on and learn how
simple and smart it is to find and fix those leaks.
TOP THREE LEAK FACTORS
* Parts installed over five years?
* Prolonged exposure to bleach in-tank cleaners?
* Visible rust or warping?"

DAVID ALEXANDER wrote:
Last week, when I got my water bill, it was a whopping $185.00. On checking
my water meter, it was spinning at the rate of about 3 gallons per minute.
I checked for anything leaking in the house and didn't find anything. The
same for the outside faucets. There's no evidence of water leaks outside,
no damp spots, etc.

My plumber came out and checked everything, but couldn't come up with
anything. I called the city water folks and one of them came out and looked
all around, even using a listening device they have. He couldn't find
anything, either, although he said the sounds were louder on the end of the
house where the septic tank and an outside faucet are located.

I haven't been able to locate the valve next to the house that turns off all
of the water, so I went home after the city water guy left, determined to
dig up my yard if needed. I went to turn off the water so we wouldn't waste
any more, and found that the meter was no longer running! I couldn't
believe it.

I called the city guy and told him that the meter had stopped, and he could
hardly believe it. We both know a leak doesn't plug itself. He had no
suggestions. I was just grateful that it had stopped.

I kept an eye on the meter for a couple of hours and it didn't budge.
However, a few hours later, just before I went to bed, I decided to check it
again and, sure enough, it was running again for no reason.

Any suggestions or analysis would be appreciated.

David Alexander