Systems and methods to filter water. A filtration device for a floodable compartment having a water inlet and a water outlet can include a removable filter for being positioned at or near the water outlet of the compartment, a strainer having a first end and a second end, wherein the first end is configured to at least partially surround the filter near the water outlet, and wherein the second end is configured to contact the compartment at least partially around the filter at a point in the compartment between the water inlet and the water outlet. The filtration device can be implemented as a water filtration system for a pool or spa, where the water inlet can be from the pool or spa, and the water outlet can be to a pump.