Water is a non-compressible medium. This means the same volume of water is required regardless of the desired pressure. Air, however, is a gas and therefore compressible.
Water-powered drilling gives high drilling performance in almost every formation
When drilling with high-pressure water, the water flows like it would in a U-formed tube (as the inner flow in the drill string goes downwards and the outer flow goes upwards in the borehole). This gives the possibility to drill in water-rich formations without problem and regardless of borehole depth.
Drilling through wood (like old foundations made of logs) is not a problem for Wassara. And when reaching an area of dense clay, the water that leaves the drill bit will simply dissolve the clay.
Water, dense clay or wooden logs in the formation doesn't affect the drilling
Why water-powered drilling have a high drilling frequency
A 4-inch air hammer, powered with 30 bar (435 psi) compressed air, will generate approximately 2 000-2 700 blows per minute and consume approximately 100 times more, 350-450 liter of air per second (618-794 cfm).
Another big difference occurs when drilling below the water table of a borehole exposed to inflowing water from the surrounding formation. A 200 m (650 ft.) deep borehole full of water is equal to a 200 m (650 ft.) water column. When drilling with an air-powered DTH system, this water column must be lifted, generating a 20 bar (290 psi) pressure loss. A water powered DTH system will not suffer from this since there is water both on the inside and the outside of the drill string. The only pressure losses that need compensating for are inside the drill string and the differences in density (water vs. slurry).