These canister vacuum cleaners allow you to use water to trap the dirt. The water takes the place of the disposable paper bag, or bagless dump cup. Some manufacturers claim that water traps 100% of dust and dirt and can take the place of disposable bags and filters. This is not entirely true. Scientific research has shown that some dust and dirt particles cannot saturate water. These particles bounce around on top of the water until they are exhausted through cracks and crevices in the machine, or settle onto the motor itself.
More Information About Water Filtration Vacuums (like Rainbow)