are two ways to find a leak using a specialised tracing gas method.
With the water supply turned off, a plumbing fitting such as a tap is
removed and a hose from the gas cylinder is attached to piping network
at this point. The gas is then turned on and allowed to flow freely
into the piping system. If there is no leak the piping system will hold
pressure, if there is a leak the gas will start to flow out of the pipe
work at the leak. The nature of the gas that we use is that it is made
up of the smallest and lightest particle known. The result is that this
gas filters through the ground/concrete or what ever the covering, to
the surface. At the surface we then trace this gas with a specialised
gas sensor that is able to pick up two parts gas per million of any
other substance (air).
With the water supply on we inject the gas under pressure into the water
system. The gas is then held in solution in the water while under pressure
and when it gets to the leak there is no further pressure to hold the
gas in solution, it now breaks away from the water particle and come
to the surface in the same way as it did above. This method came be
very dangerous as gas can have a recoil effect and should be attempted
by unqualified/untrained personal.