The Science of a Rainbow: Deconstructing the E2 Type 12 Water Filtration Vacuum

We spend up to 90% of our lives indoors, breathing air that the U.S. Environmental Protection Agency (EPA) estimates can be two to five times more polluted than the air outside. It’s a quiet, invisible battle being waged in our homes against an army of dust, pollen, pet dander, and microscopic dust mite allergens. For decades, the go-to weapon in this fight has been the vacuum cleaner. But what if the very tool designed to capture these invaders was, at times, inadvertently throwing them back into the air?

The familiar scent of a running vacuum is often not the smell of clean, but of superheated dust particles escaping through filters or microscopic leaks. This reality has pushed engineers to rethink the fundamentals of filtration. Among the most distinct and enduring of these alternative approaches is a system that swaps porous bags and cyclonic plastic bins for the oldest and most effective natural filter on Earth: water. The RAINBOW Model E2 Type 12 is a modern incarnation of this philosophy, a machine that promises not just to vacuum your floors, but to literally “wash” the air in your home. To understand its value and its quirks, we must look past its glossy black shell and dive into the physics, engineering, and history that make it work.

A Hurricane in a Water Basin

The core principle of the Rainbow system, a motto trademarked by its manufacturer Rexair since 1936, is elegantly simple: “Wet Dust Can’t Fly™.” While a traditional vacuum relies on a bag or filter to act as a physical net, the Rainbow pulls dirt-laden air directly into a basin of water. But it’s the process that happens just above the water’s surface that is the key to its ingenuity.

This is where a brilliantly engineered component called the “Separator” comes into play. Spinning at up to 23,000 RPM, it acts like a miniature, contained hurricane. As air is violently whipped into this cyclonic vortex, a fundamental law of physics takes over: centrifugal force. Imagine being on a fast-spinning merry-go-round; you feel a powerful force pushing you outwards. In the same way, the heavier dust, dirt, and allergen particles are flung outwards from the center of the air vortex. They crash into the walls of the basin and are instantly trapped in the bath of water below.

The result is a highly effective, natural filtration process. The water becomes a murky trap, locking away contaminants that can no longer become airborne. This is made strikingly clear by the LED-lit water basin, a clever piece of user-interface design that provides immediate, visceral feedback. It makes the invisible, visible, transforming the abstract concept of “clean” into the tangible evidence of dark, captured grime. Meanwhile, the now-cleansed air, being much lighter, is drawn up from the calm center of the vortex to continue its journey through the machine.

The Final Gatekeeper: A HEPA Safety Net

If water is so effective, capturing the vast majority of debris, one might ask why a second filter is necessary. The answer lies in a belt-and-suspenders approach to engineering, aimed at achieving an exceptional standard of air purity. After the air has been “washed,” it is passed through a final gatekeeper: a High-Efficiency Particulate Air (HEPA) filter.

HEPA is not a brand name, but an official efficiency standard set by the likes of the EPA. To earn the HEPA designation, a filter must be proven to remove at least 99.97% of airborne particles that are 0.3 micrometers (microns) in diameter. To put that in perspective, a human hair is about 50-70 microns thick; a single bacterium is about 1 micron. The 0.3-micron size is the gold standard for testing because it is, counterintuitively, the most difficult particle size for filters to capture, a phenomenon known as the Most Penetrating Particle Size (MPPS).

In the Rainbow system, the HEPA filter serves as the ultimate insurance policy. It is there to capture the incredibly small percentage of ultra-fine particles that might have navigated the water vortex, as well as any motor-produced particulates like carbon dust. This dual-stage filtration—a powerful liquid scrubbing followed by a medical-grade dry capture—is the scientific basis for the system’s claim as a tool for those with asthma and allergies.

An Engineering Compromise: Power, Performance, and Presence

No powerful machine is without its trade-offs, and the Rainbow E2 Type 12 is a clear case study in engineering compromises made in the pursuit of performance. Its considerable 19-pound weight and large canister form factor are not a design oversight; they are a direct consequence of its core technology. The powerful, dual-speed motor capable of generating both intense suction for cleaning and sustained airflow for air purification requires space and robust housing. The water basin itself necessitates a certain volume to be effective for cleaning an entire home.

When evaluating its power, it’s crucial to look beyond simple wattage. The listed 800-watt power consumption describes the electricity it draws, not the work it performs. True cleaning performance is better measured by metrics like CFM (Cubic Feet per Minute), which indicates airflow, and Water Lift (measured in inches), which signifies raw suction power. The system is engineered to generate high marks in these areas, enabling the power nozzle—with its combination of a spinning brush roll to agitate deep carpet fibers and rotating edge brushes to tackle baseboards—to effectively lift and transport debris into the machine.

This is the central compromise of the Rainbow: users trade the lightweight convenience of a modern stick vacuum for the deep-cleaning power, air-purifying capability, and sheer robustness of a canister system built around a basin of water. It is, by design, a substantial, deliberate piece of machinery.

A Legacy of Longevity in a Throwaway World

Perhaps one of the most compelling aspects of the Rainbow system is its history and the philosophy of longevity it represents. The manufacturer, Rexair, has been refining this technology since its founding, introducing the water-based trapping system in the mid-1930s—a time when innovation was often born of a desire to create things that would last.

This heritage is evident in the machine’s reputation for durability, with many users reporting decades of service. In an age of planned obsolescence, where electronics are often cheaper to replace than to repair, the Rainbow stands as an anomaly. It is a product from an era of design where machines were considered long-term investments. This is reflected in its high initial cost but also in a thriving market for refurbished units and readily available parts. It fosters a different kind of consumer relationship—one based on maintenance and longevity rather than disposal and replacement.

In the end, the RAINBOW E2 Type 12 is more than just a vacuum cleaner. It is a home appliance built on clear principles of physics and a consistent engineering philosophy. It leverages the power of water and centrifugal force for primary filtration and backs it up with a medical-grade HEPA filter. It unapologetically trades featherweight portability for power and multi-functionality. Understanding this—the science, the history, and the deliberate design choices—allows one to see it not as a simple purchase, but as an informed decision about how to wage the invisible, yet critical, battle for a cleaner, healthier home.