Filtration systems are BMPs that use media to remove particulates from runoff. They are typically used where space is limited, such as a highly urbanized setting. Filtration is also used to capture particular industrial or commercial pollutants such as hydrocarbons or metals, where other BMPs might be cost-prohibitive or ineffective. Filtration devices can also work well as pretreatment systems for other types of BMPs, such as pre-treatment for certain contaminants before moving water directly to ground aquifers.

Catch-basin inserts or curb inlet filters are a common example of filtration devices. When considering filtration systems, planners need to consider flow rates. In wet weather, filters must be able to treat at lest the first quarter inch of runoff, with a bypass for high-flow events. Filters may incorporate pre-settling sediment chambers to remove sediments that can clog the filters and reduce flow rates and effectiveness. Again, as with all BMPs, regular maintenance is essential.

Filtration systems can be a useful device for urban hot-spot applications where a particular pollutant is being targeted. It also can be cost-effective where land use does not allow other economical BMP options. This is particularly true with existing sites in urban settings.