my parents had their water bill go up an incredible amount...and the gas bill too...and the water heater was working over time...
and we felt a warm place on the kitchen floor...as it turns out,
there was a leak in a copper hot water line which was embedded
in the concrete slab foundation/floor. this required removing the
floor tiles, which also required removing the dish washer to get to the place to chisel...then chiselling away the cement until enough copper was exposed to replace the section that leaked, all while the
main was turned off so no other water could be used in the house
while all this went on....