[LazyPup]

That water consumption definitely looks exhorbitant. Let us consider typical water consumptions for two persons:

A shower is typically 3gal/min. thus two people taking one ten minute shower daily equals 3 gal/min x 20 minutes = 60 gal/day

A old style toilet consumes 3.5gal/flush. Allowing 6 flushes per day/ per person = 12 x 3.5gal = 42gal/day

Bathroom lavatory (hand washing, shaving, hair and cosmetic) 1.5gal x 20 times daily = 30gal/day.

You stated you had two washing machines each doing three loads a week. a wasing machine typically uses 8 gal/cycle (Wash & rinse) thus it is 6 loads x 16gal/load =96gal/week /7 = 13.71gal/day.

Dishwashing 3 gal/cycle (wash & rinse) = 6 gal 3 times daily = 18 gal/day.

cooking and food prep = 10 gal/day.

These estimates would equal 173.71 gal/day.

In your post you stated that your biling for 66 days was 78,540 gallon. For a 66 day period the above estimates would equal 11,464.96 gallon in 66 days.

78,540 minus 11,464.96 = 67,075 gals or approximtely 1000gal/day.

dividing 1000 gallon by 8gal/cu.ft = 125cubic foot of water per day.

With all due respect, i think it a waste of time to search for a leak of that dimension in the house. If you had a leak of that dimension your question would more properly be,,how do i install a sump pump.

By contrast 1 gallon of water occupies 231 cu.in, therefore the loss is 231,000 cubic inches of water.

The square root of 231,000 = 480 inches / 12"/ft= 40ft.

Thus 1 inch of irrigation on a lawn area of 40' x 40' would equal 1000 gal. day.