Why water wells lose yield

Almost every water well produces less over time. The water is usually still in the aquifer — what changes is the well's ability to let it in. Understanding where and why a well plugs is the first step in choosing a rehabilitation method that can actually reach the problem.

Specific capacity: the number that matters

Yield alone can mislead — a stronger pump can raise flow while the well keeps degrading. The honest measure of a well's health is specific capacity: flow per unit of drawdown (m³/h per metre, or gpm per foot). When specific capacity falls, the well itself is plugging, regardless of what the pump does. Every rehabilitation should be measured by specific capacity before and after, using a step-drawdown test.

Chemical incrustation

As water flows toward a well, pressure drops near the screen. That pressure drop releases dissolved carbon dioxide, shifts the water chemistry, and causes minerals to precipitate — most commonly calcium carbonate, and iron and manganese oxides. The deposits form exactly where flow concentrates: on the screen, in the gravel pack, and in the surrounding aquifer. Typical incrusting materials include calcium carbonate, ferric hydroxide and oxide, manganese hydroxide, silica, and metal sulphides.

Iron and biofouling

Iron in groundwater feeds naturally occurring iron bacteria — Gallionella and Crenothrix are the most common. When drilling changes their environment, these bacteria multiply around the screen, producing a corrosive biofilm ("biofouling") of living and dead cells bound in iron hydroxide. Sulphate-reducing bacteria can add to the problem in low-oxygen conditions. Biofouling both clogs the screen and corrodes it. Wells with high iron content and iron bacteria are among the most aggressive plugging cases — and a frequent reason conventional cleaning gives only short-lived results.

Where the plugging actually sits

This is the decisive point for choosing a method. In most aging wells the restriction is not just a film on the inner screen surface — it extends through the screen slots, into the gravel pack, and into the near-wellbore zone. A method that only cleans the inner screen face (for example, jetting or brushing alone) can leave a well looking clean on camera while its specific capacity barely recovers, because the blockage sits beyond that method's reach.

What this means for rehabilitation

Because incrustation and biofouling develop through the screen and into the pack and formation, effective rehabilitation has to deliver energy — and, where needed, chemicals — into those zones, not just against the screen wall. That is the physical basis of impulse rehabilitation.

Diagnosis depends on the specific well: its construction, geology, water chemistry, and history. Every recommendation begins with the well's records and test data.