Quick answer: when a DTH hole starts taking groundwater, the main operating problem is not simply that the hole is “wet.” Water can add back pressure at the hammer, change cuttings transport, wash or dilute the lubricating oil film, and turn fine cuttings into a heavier slurry. The correct response is to identify where the water is entering, estimate the water head above the hammer, confirm that the compressor can still deliver the hammer’s required airflow at operating pressure, and then adjust flushing, feed and rotation only within the hammer and rig manufacturer’s limits.
For mines, quarries, contractors and water-well crews, the costly mistake is often to react to a water strike by increasing compressor pressure without checking the whole air-and-return path. A wet hole may need more available pressure to overcome back pressure, but it may also need more effective cuttings evacuation, different flushing practice, tighter control of lubrication and closer monitoring of unstable or clay-bearing zones.
What changes when a DTH hole becomes water-bearing?
Water-bearing rock can mean several different field conditions: a small seep through joints, a localized fracture that produces a strong inflow, a deep standing water column above the hammer, or a formation that produces water together with clay, sand or fines. These conditions do not create the same drilling response.
| Observed condition | Likely drilling effect | First checks | Main risk |
|---|---|---|---|
| Small water seep with normal cuttings return | Limited change in hammer response | Pressure trend, lubrication delivery, cuttings condition | Gradual oil-film washout or corrosion if ignored |
| Strong fracture inflow | Back pressure rises; cuttings may become slurry | Water-strike depth, pressure at rig, delivered airflow, return path | Penetration loss and poor hole cleaning |
| Deep standing water column | Hammer works against hydrostatic head | Water-column height above hammer and compressor pressure reserve | Insufficient effective pressure at the hammer |
| Water plus clay/fines | Sticky cuttings can pack around tools | Return flow, mud rings, torque/rotation changes, hole stability | Stuck drill string or blocked return path |
| Intermittent cavities/fractures | Air and water return may change suddenly | Penetration trend, pressure changes, loss of circulation | Unstable drilling and difficult hole cleaning |
1. Distinguish formation water from intentional water injection
Formation water enters the borehole from the rock. Intentional water injection is added by the drilling system for dust suppression, flushing or other operating reasons. They may occur at the same time, but they should not be treated as the same variable.
When the hole first becomes wet, record the depth and the change in returns before changing settings. A sudden increase in water return at a fracture can indicate a new formation inflow; a gradual change may come from accumulated water in the borehole. If the rig also injects water, record that rate separately. This distinction helps the crew determine whether a pressure change is caused by the geology, the flushing system or both.
Mincon’s current hammer-life guidance also notes that water injection changes lubrication conditions inside a DTH hammer and that oil delivery should be adjusted according to the manufacturer’s wet-drilling guidance. That is a maintenance requirement, but it also matters to performance because the oil film helps seal internal clearance paths.
2. Account for groundwater back pressure at the hammer
Water above the hammer creates hydrostatic back pressure. Halco’s A–Z of Drilling gives a practical field rule: approximately 1 bar (14.5 psi) of back pressure for every 10 m (33 ft) of water head. This is a first-order estimate for a water column; actual pressure behavior at the rig can also be affected by dynamic flow, fractures, foam, cuttings, pipe size and restrictions.
That means a hammer working beneath a substantial water column may see less effective pressure differential than the compressor gauge alone suggests. Do not simply add a fixed amount of compressor pressure. Instead:
- Estimate the water head above the hammer.
- Confirm the hammer manufacturer’s required operating pressure and airflow.
- Check the compressor’s delivered flow at the intended pressure, not only its free-air rating.
- Allow for line, valve, joint and drill-string losses.
- Compare rig-gauge pressure and penetration before and after the water strike.
- Stay within the compressor, rig, hammer and drill-string pressure ratings.
If the compressor does not have enough pressure-flow reserve, increasing the pressure set point may not restore performance because delivered airflow can fall as the system approaches its operating limit.
3. Hole cleaning becomes a water-and-cuttings transport problem
Compressed air must both power the DTH hammer and carry cuttings out of the annulus. In a wet hole, broken rock mixes with water. Fine or clay-rich material can become heavier and more cohesive than dry cuttings, while a high inflow can increase the mass that must be lifted out of the borehole.
Watch the returns rather than relying on one pressure number. Warning signs include:
- cuttings becoming thick, muddy or intermittent;
- penetration falling while the hammer still sounds active;
- pressure rising or fluctuating after a water strike;
- the drill string becoming harder to rotate or lift;
- reduced cuttings volume at the collar despite continued drilling;
- repeated need to stop and clean the hole.
Legacy DTH operating manuals from Secoroc describe foam as one possible method for suspending cuttings and formation water where back pressure and hole cleaning are difficult. Foam is not a universal remedy: use it only where the rig, hammer, environmental requirements and site procedure allow it, and follow the relevant OEM instructions.
4. Do not confuse pressure with airflow reserve
A DTH hammer datasheet usually specifies air consumption at stated operating pressures. The compressor must therefore be evaluated as a pressure-flow pair. In a water-bearing hole, the required pressure at the hammer may effectively increase because of back pressure, while the cuttings-transport demand can also increase.
The practical question is not “What compressor pressure do I have?” but “How much air can the compressor still deliver at the pressure required by this hammer under this water head and site condition?”
| Field symptom | Possible air-system cause | Check before changing tools |
|---|---|---|
| Hammer slows immediately after water strike | Back pressure reduces effective pressure differential | Water head, operating pressure, compressor flow at pressure |
| Pressure gauge rises but cuttings return worsens | Return path is restricted or water/cuttings load has increased | Annulus, flushing passages, mud rings, hole condition |
| Pressure falls and hammer becomes weak | Insufficient compressor reserve, leakage or increased hammer air demand | Compressor output, hoses/joints, hammer condition, water effect |
| Cuttings return is poor despite normal pressure | Air velocity or return path may be inadequate | Pipe OD, hole diameter, airflow, depth, water volume |
5. Wet drilling changes hammer protection requirements
Water can wash the lubricating oil film from internal hammer surfaces. Mincon’s 2026 guidance specifically warns crews using water injection to pay attention to where water enters the air stream and to increase oil volume as required by the operating guidance. Older Mincon and Secoroc hammer manuals also treat wet drilling as a condition requiring more lubrication than dry drilling.
Do not apply one universal oil multiplier across brands and hammer models. Use the current hammer manual and the actual airflow. During operation, confirm that lubrication is reaching the hammer, and after prolonged wet drilling follow the OEM shutdown/storage procedure so moisture is not left inside the tool. The objective is to prevent corrosion, galling and power-robbing internal leakage.
6. Water can turn weak ground into a hole-stability problem
The presence of water is especially important when the formation contains clay, sand, weathered zones or broken rock. Epiroc notes that clay can swell when water is introduced and that sand can collapse around drilling equipment; both conditions can contribute to tools becoming stuck.
If a wet interval is also unstable, the correct operating priority may shift from maximum penetration to maintaining a usable hole. Watch for rising torque, difficult pullback, worsening returns, repeated bridging or a sudden change in penetration. Do not force the drill string through a condition that is already packing around the tools. Site-specific casing, foam, flushing or hole-support methods may be required and should be planned with the rig/OEM procedure.
7. A practical field workflow after hitting groundwater
- Mark the water-strike depth. Record the depth where returns first change and whether the inflow is continuous or intermittent.
- Establish the baseline. Note penetration rate, RPM, feed, rig pressure and cuttings return immediately before and after the strike.
- Estimate water head. Use the standing water column as a first-order back-pressure check; do not treat the estimate as a substitute for pressure measurements.
- Check compressor reserve. Confirm delivered airflow at the intended operating pressure and site altitude.
- Inspect the return path. Look for thick slurry, blocked flushing holes, mud rings, excessive annular restriction or unstable ground.
- Verify lubrication for wet operation. Follow the current hammer manufacturer’s oil type and wet-drilling rate guidance.
- Adjust one variable at a time where practical. Avoid simultaneously changing pressure, feed and rotation because the crew will not know which change helped.
- Stop if the hole becomes unstable or the string begins to stick. Protecting the drill string and hole can be more valuable than forcing another metre.
Common mistakes in water-bearing DTH drilling
- Increasing pressure without checking airflow. The compressor may not deliver enough flow at the higher pressure.
- Ignoring the water head. A deep water column can materially reduce effective pressure at the hammer.
- Treating all wet holes alike. A small seep, a high-flow fracture and water-plus-clay require different responses.
- Watching only the pressure gauge. Cuttings return, penetration, torque and pullback behavior are equally important.
- Using dry-drilling lubrication practice in sustained wet conditions. Follow the hammer OEM’s wet-drilling lubrication requirements.
- Continuing to drill through a packing or collapsing interval. Water can aggravate clay or sand-related sticking risks.
What to include in an RFQ for a water-bearing application
For a useful technical quotation, send enough information for the supplier to understand both the DTH system and the water condition:
- rig make/model and drilling method;
- exact DTH hammer make/model and required bit shank;
- target hole diameter, total depth and inclination;
- drill-pipe OD, bore and connection;
- compressor model plus rated airflow at intended pressure;
- site altitude;
- rock type, fracture condition and any clay/sand intervals;
- depth where groundwater is normally encountered;
- estimated inflow or observed water-return condition;
- whether intentional water injection or foam is used;
- current penetration rate and pressure behavior before/after the water strike;
- inspection, packing and documentation requirements.
For current PerfoMax options, review the DTH Tools collection and the DTH Drill Bit Selection page. Final hammer/bit compatibility and operating limits should be confirmed from the exact model, shank drawing and approved quotation.
Frequently asked questions
Can a DTH hammer drill through groundwater?
Yes. DTH hammers are widely used in water-well and other water-bearing applications. Epiroc’s 2026 DTH 5 field story, for example, describes a water-well job where water was encountered at depth and drilling continued. The setup still has to account for water head, compressor capability, hole cleaning and hammer lubrication.
Why does penetration rate drop after the hole hits water?
Possible causes include groundwater back pressure, reduced effective pressure at the hammer, insufficient airflow at the new operating condition, heavier wet cuttings, a restricted return path, a change in formation strength or changes in internal lubrication/sealing. Check these before assuming the bit or hammer must be replaced.
How much back pressure does groundwater create?
As a field estimate, Halco’s A–Z of Drilling uses about 1 bar (14.5 psi) for every 10 m (33 ft) of water head above the hammer. Treat this as a hydrostatic approximation; actual dynamic conditions can differ.
Should I increase compressor pressure when I hit water?
Not automatically. First compare the estimated water head with the hammer’s required operating pressure and confirm that the compressor can still deliver the required airflow at that pressure. Also check return-path restriction and site pressure limits.
Can foam help clean a wet DTH hole?
In some applications, yes. DTH operating guidance has used foam to suspend cuttings and formation water and to assist hole cleaning at lower air velocity. Use only products and procedures approved for the rig, hammer, geology and environmental requirements.
Need a DTH setup for a water-bearing formation?
Send PerfoMax your hammer and bit interface, hole diameter and depth, compressor pressure-flow data, site altitude, rock condition and the depth/behavior of groundwater. We can use those inputs to prepare a configuration for technical confirmation before quotation. Request a quote / technical review.