It is a combination of the tungsten-tipped bit being turned and hammered, like a larger version of a hand-held hammer drill, that allows it to drill through the toughest rock.
"The exhausted air from the hammer blows the drilled material back up to the surface to keep the bit clear," John says.
"The rig will drill a six to 12-inch hole and is equipped to drill to 1,200 feet, but the deepest we go is 600 or 700 feet for geothermal heating applications," Myles says.
"We start with an eight-inch bit and drill from the surface down through the overburden to the bedrock and into it," explains John.
On the job in Co Wexford it took just one four-metre (13ft) long liner to line the borehole from the surface through the overburden and into the bedrock.
"Around the coast of Wexford you could have to use 250ft of steel liner to get to the bedrock. Each one has to be welded together to make a solid tube as they go down," Myles explains.
With the liner in place, the lads changed the drill head from an eight-inch to a six-inch and fed the drill down through the liner. Then they continued drilling into the bedrock until they hit water.
In this case they hit it at 120ft and drilled an extra 40ft for reserve. Myles estimated that the water being blown to the surface would give a supply of around 500 gallons/hour.
To achieve this depth an extra 20-foot drilling rod had to be added from the carousel beside the rig each time the drill progressed down into the bedrock. At this site the bit progressed at about 20ft every seven minutes.
For my sake they were initially adding water to the compressed air to keep the dust down for taking pictures, but this slowed progress.
This is a practice necessary for drilling in a village or town, or close to other properties.
With all the rods disassembled and back on the carousel, and the drill bit back on the rig, the well had to be lined with piping to keep debris out.
There are slits cut in the piping that let the water into the borehole from all heights.
The pipe is fed in manually and lowered with a rope to the bottom. With all their work done, a temporary lid is welded onto the top of the steel liner ready for the pump man.
There are a number of difficulties which can be encountered when drilling.
"Sometime you get cavities in the rock and they start caving in. In that case you might have to use the under-reamer," Myles says.
"The under-reamer is a bit that can be fed down through the liner and opens out under the liner when you start drilling."
It is used where the ground is bad and goes from rock to soil and back again.
In these conditions the under-reamer brings the liner down with the hole into the bedrock, where it is possible to start drilling again.
While the O'Rourkes work principally in the south-east, they have just come back from the west where they spent a couple of weeks working.
"In Galway the rock is tough, it's mostly very hard limestone and it's very hard to get water, and the overburden would be rough too," says Myles.
"There is lots of gravel and boulders in the overburden. With boulders, if you don't hit them straight on, the bit can go off (crooked) and then you go install the liner and it bends in the liner because you can't get it straight down."
Generally it costs €10/ft to drill a well but Myles says the cost increases when a lot of steel lining is required.