Why the drilling flow is not the operating rate
Almost every borewell owner remembers the moment water came up during drilling. The compressor blew a strong stream from the hole and everyone was pleased. That observation is real, but it is not a pumping rate.
During drilling and airlift development, water is lifted by compressed air. The quantity depends on the compressor’s pressure and free air delivery, the depth of the air line, the submergence, the hole diameter and the discharge arrangement. A typical borewell compressor working at 200–400 psig (13.8–27.6 bar) and 600–1,500 cfm can lift a large volume for a short period, often from water stored in fractures close to the well. It says little about how the well will behave when a submersible pump runs for eight or twelve hours a day, every day, through the dry season.
The drilling record should be kept as a construction record. The operating rate should come from a controlled pumping test and the user’s real demand.
Four numbers that must be kept separate
Much confusion comes from writing one number in a field called “capacity”. Four different quantities are involved.
| Quantity | What it describes | Where it comes from |
|---|---|---|
| Observed test discharge | Flow during a defined test, for a defined period | Pumping test record |
| Operating discharge | Flow selected for routine use | Engineering decision based on test and demand |
| Pump capability | Flow the pump can deliver at the actual total head | Pump curve and installation |
| Permitted abstraction | Any limit set by a permission or scheme rules | Authority or owner conditions, where applicable |
The operating rate must respect all four. A pump able to deliver more than the well can sustain will draw the water level down to the intake. A rate the well can sustain may still exceed what the owner is permitted or needs to abstract.
Start from demand, not from the biggest flow
Before looking at test results, define what the water supply must achieve:
- daily volume required, and how it varies across the year;
- the peak demand period, for example morning use in housing or irrigation windows on a farm;
- usable storage in tanks or sumps;
- acceptable interruption and any alternative supply;
- whether the pump will be supervised, run on a timer or run automatically on level control.
Storage changes the decision. A lower rate over longer hours with a tank can meet the same daily volume as a high rate for a few hours, while drawing the well down less. In rural Telangana and Andhra Pradesh, where power for agricultural pumping is often available only in set hours, the schedule itself may be the governing constraint.
Build an evidence sheet for the decision
The evidence for a rate decision should include:
- The well identity, pump, intake setting depth and discharge measurement point.
- The time series of discharge and water level during the test, not just the final reading.
- Recovery readings after the pump stopped.
- Any interruptions or rate changes during the test.
- Season of the test, and whether neighbouring wells were running.
- Water quality and sand observations, with how they were sampled.
- The pump’s curve and the measured delivery head.
A single final reading can hide a continuing decline. A pumping water level still falling at the end of a short test suggests the rate may not be sustainable over longer periods. Slow or incomplete recovery points the same way. A clear discharge does not prove the water is chemically or microbiologically suitable; that needs testing for the intended use. See borewell yield testing and production duty for test methods.
Express the operating rate as an envelope
A useful instruction combines several limits rather than a single figure. A typical operating sheet might set:
- a normal flow setting, with a tolerance;
- a maximum continuous run time before a rest period;
- a minimum pumping water level, or a pump intake margin, protected by a dry-run or level cut-out;
- a daily or monthly volume limit, where demand or permission requires it;
- a sand or turbidity condition that requires the pump to be stopped and investigated.
The values must be chosen for the site by the responsible engineer; no general article can supply them. Where two limits conflict, use the more restrictive one until the conflict is reviewed. Avoid setting the rate as a fixed percentage of the tested maximum; the governing constraint may change between seasons or after a pump change.
Revision triggers: when the rate must be reviewed
An operating rate is valid only while the conditions behind it hold. Agree in advance which events trigger a review.
| Trigger | Why it matters | Typical response |
|---|---|---|
| Pumping water level deeper than baseline at the same flow | Well or aquifer under more stress | Reduce rate or hours; investigate |
| Dry-run or low-level trips become frequent | Rate exceeds what the well supplies at that setting | Review rate and pump setting |
| Sand or turbidity increases | Possible over-pumping or screen damage | Stop and inspect |
| Pump or motor replaced | Different curve and head relationship | Re-test and confirm settings |
| New neighbouring borewell or change in nearby pumping | Interference can lower water levels | Monitor and review |
| Dry season or failed monsoon | Lower water table | Seasonal review of limits |
| Change in demand or storage | Schedule and volume needs change | Recalculate duty |
| Well deepened, flushed or redeveloped | Well characteristics change | New test and new decision |
Keep a simple monthly log of flow, pumping water level, run hours and trips so that these triggers are noticed early. A review is far cheaper than a burnt motor, a sand-damaged pump or a well that has been pumped beyond what it can recover from during the dry season.
Name who is allowed to change the rate. A temporary setting used during commissioning must not become the permanent unattended setting by default.
When redevelopment or deepening is needed
Over years, a borewell’s performance can fall because of fine material clogging fractures, scale, or a falling water table. Sometimes the right response is a lower operating rate. Sometimes the well is flushed or redeveloped with a compressor, or deepened with a drilling rig. Each of these needs the right compressor: flushing and redevelopment often use a portable or borewell compressor with suitable pressure and an air line set at the right depth, while deepening uses the full drilling compressor, typically 600–1,500 cfm at 200–400 psig (13.8–27.6 bar) and up to about 35 bar (507.6 psig) for special units.
After any such work, the old operating rate no longer applies. Carry out a new test and issue a new decision, keeping the earlier records for comparison.
How Reddy Compressors helps
We supply borewell compressors of all types and many makes: new machines, used and refurbished units, rentals, service and spare parts. We are an independent multi-brand specialist covering ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and others, not an authorised dealer of any brand. We have tie-ups with all major and reputed brands.
The operating-rate decision itself belongs to the owner’s engineer and pump specialist. Our role is the compressed air that makes the well and keeps it productive:
- selling and hiring borewell compressors for drilling, deepening and redevelopment;
- advising on pressure and flow for the hammer, bit size and depth;
- servicing drilling compressors so they deliver their rated pressure;
- supplying spares identified from the nameplate and the old part.
Our office is at Tarnaka, Secunderabad. Our team of more than 20 service engineers and technicians covers Telangana and Andhra Pradesh, and we supply across India. See borewell compressor rentals and hire and new borewell compressor sales.
What to send us
- Whether you need drilling, deepening, flushing or redevelopment air.
- Hole diameter, current depth and target depth.
- Static water level and expected water ingress, if known.
- Rig and hammer details.
- Site location and how long you need the compressor.
- Existing compressor nameplate photo, if service or spares are needed.
Frequently asked questions
How do I know the safe pumping rate for my borewell?
The safe rate comes from a controlled pumping test, not from the flow seen during drilling. Watch whether the pumping water level stabilises at a given flow and how quickly it recovers when pumping stops. Then compare that with your daily demand and storage. A qualified engineer or experienced pump contractor should set the rate and the protective limits for your particular well.
Why did my borewell give more water during drilling than with the pump?
During drilling, the compressor lifts water with high-pressure air, often from water stored in fractures close to the hole, for a short time. A submersible pump runs for hours and depends on how fast the aquifer can refill the well. The two are different processes, so the airlift flow is usually not a reliable guide to long-term pump output.
Should I run my borewell pump for fewer hours at a higher flow or longer at a lower flow?
Where storage allows, a lower flow over longer hours usually draws the well down less and is gentler on the well and pump. However, the pump must still operate within its curve and the motor needs adequate cooling flow. Power availability, especially for agricultural supply, may also limit hours. The right answer depends on your test results and schedule.
When should a borewell operating rate be changed?
Review the rate when the pumping water level is deeper than before at the same flow, dry-run trips increase, sand appears, the pump or motor is replaced, a neighbouring borewell starts pumping, the dry season sets in, demand changes, or the well is flushed, redeveloped or deepened. Agree these triggers in advance and name who may change the setting.
Can a compressor be used to improve an old borewell’s yield?
A compressor can be used to flush or redevelop an older borewell by removing fines and debris from fractures and the hole, which sometimes improves performance. Results vary with the formation and the cause of decline, so no outcome can be promised. After redevelopment, carry out a fresh pumping test and set a new operating rate rather than reusing the old one.
What compressor is needed to deepen an existing borewell?
Deepening needs a full drilling compressor matched to the hammer, bit size and target depth, typically 600–1,500 cfm at 200–400 psig, about 14–28 bar, with special units up to about 35 bar. Deeper holes and wet holes need higher pressure. We can advise on the pressure and flow, and supply a machine to buy or hire.
Related pages
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.