Which of the following is most likely a cause of decreasing drawdown and an unchanging static water level?

In assessing the situation where there is a decreasing drawdown and an unchanging static water level, the most plausible explanation is that the pump is losing efficiency.

When a pump decreases in efficiency, it struggles to lift the same volume of water as it did previously. As a result, even if the static water level remains unchanged, which indicates the water level in the aquifer is stable, the amount of water that the pump can draw from the well may decrease. This manifests as reduced drawdown, meaning that while the static water level does not move, the amount of water that can be pumped from that level is diminished.

Conversely, aspects such as increased water demand or over-pumping tend to decrease both drawdown and dynamic water levels, while changes in water quality might not directly relate to the physical pumping dynamics in this specific scenario. Thus, a loss of efficiency, leading to a failure to extract the same quantity of water despite a stable static level, directly aligns with the observation of decreasing drawdown.