There are basically two types of pond pumps to choose from - externally mounted and submersible. External pumps were traditionally used in water gardens. They sit outside the pond, with a hose that leads from a strainer in the pond to the pump. From there the water is forced either to a waterfall, stream or fountain. Because external pond pumps are often noisy and require extra plumbing, they are usually not suited for most backyard ponds. Due to easier accessibility and ease of repair, however, external water pumps are often the best choice for larger water gardens and public installations. Submersible water pumps are usually preferred by most do-it-yourselfers. They sit underwater where they are quiet and unseen. These pumps are easy to install, require no priming and stay cool thanks to the surrounding water. Submersible pumps draw water from the bottom of the pond, either through a strainer or biological filter. A hose attached to the outlet then feeds water to whichever water feature you have installed.