There are three main stages to stormwater treatment and management. All three systems when combined form a complex but efficient treatment system that is able to remove almost all contaminants and pollutants, both physical or dissolved. The first stage is the primary treatment stage. This stage incorporates the removal of larger debris and trash and is usually seen as a gross pollutant trap. This stage is a vital part of the process as it is the first line of the defence for the stormwater management system with the larger more damaging pollutants being removed at this point. These systems mainly focus on the physical processes of filtration such as physical screeninghydrodynamic separation and sedimentation. This primary process is designed to increase the longevity of the system, reducing maintenance frequency, reducing sediment load and maintaining steady flow of water.

The second stage in the treatment process is the secondary treatment stage. This stage is mainly focused on attempting to achieve a certain degree of effluent quality by using processes to remove fine particle sedimentation, settling chambers and oil removal. These pollutants that are removed are all typically classified as non-attached pollutants such as sediment and oils. The most commonly used systems that are seen as secondary treatment systems is the oil separator and coalescing systems.

The final step in the stormwater management system is the tertiary treatment systems. These systems are usually classified by enhanced sedimentation and filtration, biological uptake, adsorptionand chemical filtration processes. The pollutants that are usually aimed to be removed are nutrients, heavy metals, phosphorus, attached particles and bacteria. These systems are usually much more complex, using a range of media using a variety of chemical processes to remove miniscule particles and attached pollutants. This processes is usually the final processes that are designed to improve the effluent which has resulted from the previous primary and secondary treatment process. After this final process is completed and the desired pollutant levels are achieved the water is returned to the environment, to water storage or retention basins.