Hydro-Action is a U.S.-based manufacturer of residential aerobic septic systems, best known for developing one of the early compact aerobic treatment unit (ATU) designs in the late 1980s.

Their systems use an extended aeration activated sludge process, where air is continuously introduced into wastewater to support aerobic bacteria that break down organic material. A defining feature of Hydro-Action units is their internal circulation and mixing design, which keeps solids suspended and improves treatment efficiency within a relatively compact tank.

These systems are compatible with most linear style air pumps (Hiblow & FujiMAC) and typically have a 1/2HP bottom or mid suction pump.  

Hydro-Action is a Registered Trademark of A.K. Industries, Inc