A tube settler is a water treatment device used to improve the settling process during the sedimentation phase of water treatment. It consists of a series of tubes or channels, typically made of lightweight plastic materials like PVC, arranged in a compact, inclined manner within a tank or basin. These tubes or channels are designed to increase the effective settling area for a given footprint, enhancing the efficiency of the sedimentation process by accelerating the settling of suspended particles from water or wastewater.

The principle behind tube settlers is based on reducing the vertical distance that particles need to settle before being removed from the water column. As water flows upward or downward through the inclined tubes, particles settle on the tube walls and slide down to the bottom due to gravity, thereby clearing the water of solids more effectively than in conventional sedimentation basins.