Well Completion

Water Well Development and Testing: How to Prove the Yield Before You Set the Pump

By Windrilling Technical Team – Updated October 2026 – 13 min read

I once watched a crew pack up and drive away from a well that was producing sand. They had cased it. They had gravel packed it. The screen size was right. Nobody had developed it.

Two days later the pump was destroyed. Six weeks later the owner was drilling a second hole next to the first one, convinced the ground was bad.

The ground was fine. The well was never cleaned.

People treat development and testing as the tidy-up after the real work. It is the opposite. Development is what turns a hole with casing in it into a water well, and testing is what tells you whether the money you spent was a good decision or an expensive lesson.

Why Development Is Not a Formality

Drilling leaves a mess behind it. A mud rotary hole is lined with a filter cake of bentonite and fines. A DTH hole is full of dust and cuttings that were never fully lifted. Around the screen there is a zone where the natural grading of the aquifer has been disturbed.

Leave that in place and three things happen at once. The well yields less than the aquifer can give. It keeps making sand. And the pump works harder for less water, which shortens its life.

Development reverses all three. It removes the wall cake. It pulls fines out of the formation near the screen. It regrades the material immediately around the screen so the aquifer itself becomes the filter.

The Four Methods You Will Actually Use

Method	What it is good at	Equipment	Watch out for
Over-pumping and surging	Opening up a naturally graded sand and gravel aquifer	The production pump or a test pump	Do not over-pump so hard that you dewater the screen
Airlifting	Cleaning mud rotary wells, washing screens, lifting fines	Air compressor and an air line	Air pressure must suit the submergence depth
Jetting	Breaking up wall cake at the screen, washing behind the pack	High pressure pump and jetting tool	Easily damages a light PVC screen if misused
Bailing and surge block	Tight wells, low yield, where you must be gentle	Bailer or surge block on a line	Slow. Expect repetition, not one pass

Over-Pumping and Surging

The simple version is to pump harder than the well will be worked later, then stop, then start again. The on-off cycle drives water in and out of the screen. That movement pulls fines through and leaves the coarser material behind.

The discipline is in the stopping. If you draw the water level below the top of the screen, you stop cleaning and start pumping air. Sand production also rises sharply when you overdo it, which is the opposite of what you want.

Airlifting

Airlifting is my default for a mud rotary well, and it is the one method that reliably cleans a screen that has been smeared with wall cake. You run an air line down inside the casing. Air mixes with the water column, the mixture becomes light, and it rises. Water and cuttings come out of the top.

The whole method depends on submergence. The air injection point has to sit deep enough below the working water level for the air to lift a real column of water. Too shallow and you get bubbles and nothing else. There is a practical rule of thumb about the ratio of submergence to lift, and every operator has a version of it, but the principle is simple: more submergence, more lift.

This is where the compressor stops being an accessory. Airlift development is a compressed air job, and the required air volume rises with the casing size and the depth of the water column. Our TDS C600 air compressor is the entry unit we quote for shallow and mid-depth development work, with larger models for deeper strings. If you are not sure which size you need, the air requirement is worth working out with us before you buy anything.

Jetting

A jetting tool directs a high pressure stream sideways through the screen. It breaks the wall cake and washes the formation just outside it. Used well, it is fast and precise. Used badly, it cuts a groove in the formation or punctures the screen.

Keep the pressure modest, keep the tool moving, and never hold it in one place. If you are working through a light PVC screen, this is the method where a mistake shows up immediately.

Bailing and the Surge Block

A bailer is a simple tube with a flap. You drop it, you fill it, you haul it up. A surge block does the same job with a piston action, pushing water out through the screen and pulling it back. Both are slow, and both are kind to a fragile well.

When a well is shallow and low yielding, this is often the only method that will not make things worse. Expect to repeat the cycle many times. Nobody finishes a surging job in one pass.

Dispersants, and When Chemicals Help

Some clays are stubborn. A dispersant or a mild acid wash can break down drilling fluid residue that plain water will not move. It works. It is also the part of completion where I stop giving blanket advice.

Anything you put down a well can come back out of a tap. If the well is for drinking water, agree the chemicals and the neutralisation steps with the client and with whoever regulates the supply. Get it in writing. A cheap dispersant is not cheap if the well has to be condemned.

How You Know Development Is Finished

There are three signs, and you want all three before you call it done.

1. The water runs clear. Not clear-ish. Clear, at the discharge, after a sustained pumping period.
2. The sand content is under control. Measure it, do not eyeball it. A measured sand content test protects you later, when the client says the well was always sandy.
3. The drawdown stabilises. When you pump at the same rate twice and get the same water level both times, the near-well zone has stopped changing.

A well that is still making sand after full development is not a development problem. It is a screen or gravel pack design problem, and it belongs with the casing programme. If that is where you are, read our guide on choosing water well casing and screen for boreholes before you order anything else.

The Step Drawdown Test

The step drawdown test is the cheapest piece of information you will ever buy about a well, and it is the one most often skipped. You pump at a series of increasing rates, hold each rate long enough for the water level to settle, and record the drawdown.

Published test procedures differ in the details, but the shape is consistent. Most guidance describes something like three or four steps, each held for a period on the order of one to two hours, starting at the lowest rate. Some procedures run shorter steps for a quick assessment; others go longer. What you must not do is change rate before the level has settled, because then you are measuring your own impatience.

The test gives you two things. It shows how the well behaves at different rates, and it exposes the well loss component, which is the part of the drawdown caused by the well itself rather than by the aquifer. A well with high well loss is telling you something is wrong at the screen face.

One field warning that costs people a whole test: do not draw the level below the pump intake. Air enters the pump, the discharge drops, and the test is spoiled. If it happens, shut down, let the well recover to static level, and start again at a lower rate.

Constant-Rate Pumping and Recovery

After the steps, many programmes run a constant-rate test at the intended working rate for a longer period, then stop the pump and watch the water level climb back. That recovery curve is the most honest measurement you will get, because recovery is undisturbed by pumping.

Record water levels on a fixed schedule during both phases. A handful of readings taken at random times is not a test, it is a story. Water level, time, discharge rate, sand reading. Every line.

Specific Capacity and Well Efficiency in Plain Numbers

Two simple numbers tell you most of what you need to know about a completed well.

• Specific capacity. Divide the pumping rate by the drawdown. If you pump 10 litres per second and the level drops 5 metres, the specific capacity is 2 litres per second per metre of drawdown. It is the well equivalent of fuel economy.
• Well efficiency. Compare the drawdown you measured against the drawdown the aquifer alone should produce at that rate. The gap is well loss. Both numbers are normally worked out from the step test data.

I prefer specific capacity in the field because anybody can compute it and it never lies about trends. Write it down on the day the well is commissioned. In three years, when yield has fallen, that number is how you prove whether the well is failing or the pump is.

Record	Why it matters later
Static water level before test	Baseline for seasonal and long-term change
Drawdown at each step rate	Reveals well loss and correct pump sizing
Final constant rate and stabilised drawdown	Sets the sustainable working rate
Specific capacity	Single number for future comparisons
Sand content at end of test	Protects you in any later dispute
Recovery time to static	Distinguishes a tight aquifer from a damaged well

Setting the Pump at the Right Depth

Pump setting depth comes straight out of the test. You want the intake far enough below the pumping water level that the pump never sucks air, and high enough above the bottom of the well that it does not sit in settled sand.

Get this wrong and the symptoms look like an aquifer problem: intermittent discharge, motor overheating, sand in the tap. It is usually a setting depth that was decided by habit rather than by a test.

What to Hand the Client

A completion report is not paperwork. It is the difference between being trusted on the next contract and being blamed for the last one.

1. Depth and diameter of each hole section, and the casing and screen installed in it.
2. Screen type, slot size and the grading data behind the choice.
3. The development method used, and for how long.
4. Step test rates, drawdowns and the recovery record.
5. Specific capacity, recommended working rate and maximum recommended rate.
6. Sand content at completion, with the method used to measure it.
7. Recommended pump setting depth and the water level it is based on.

The drilling programme that produced the hole matters just as much as the completion record. If you are still planning the borehole, our step-by-step water well drilling process guide sets out where each stage sits, and the mud pump sizing guide covers the equipment side for rotary work.

Questions I Get Asked Most

How long should development take?

As long as it takes for the water to run clear and stay clear. A clean sand and gravel aquifer can come good in hours. A mud rotary well in a clay-rich formation can take much longer. Anyone who quotes you a fixed number of hours is describing a habit, not a well.

Can I skip the test if the water looks fine?

You can, and it will feel like a saving until the pump burns out or the client asks what the well actually yields. A step test is cheap. Guessing the setting depth is not.

Do I need a compressor for development?

Not for every well, but for mud rotary work and screen cleaning it is the tool that does the job properly. If you already own a crawler or truck mounted rig for water wells, the compressor is usually the next item on the list, because it also supports DTH drilling.

The well yields less than the survey promised. What now?

Re-develop it before you re-drill it. A surprising number of low-yield wells are simply under-developed, and a second, more thorough development pass costs a fraction of a new hole. Test after, so you know which of the two fixed it.