Rainwater collection is supposed to be simple—set up a barrel, catch the drops, water your plants. But anyone who’s tried it knows the messy reality: leaves, twigs and roof grit clogging filters faster than you can say “downpour.” This clever solution by NeedItMakeIt consists of a 3D-printed self-cleaning water filter, inspired by hydroelectric systems, that promises to keep your rain barrel flowing without the hassle.
The concept is based on the Coanda effect, where water clings to curved surfaces, allowing clever engineering to separate liquid from debris. Traditional Coanda filters, found in hydroelectric plants, use slanted, fin-like structures to guide water through narrow gaps while letting heavier debris slide off. NeedItMakeIt took this idea and reimagined it for the humble downspout, designing a filter that could fit into a home rainwater system. The goal? A near zero-maintenance setup that delivers clean water to your barrel while sending leaves and twigs on their merry way.
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Early designs started with a flat, sloped surface fitted with angled slats, like a miniature staircase for water. As water flows down, the slats shear off thin layers, capturing the liquid while debris continues its descent. Testing this prototype outside with a garden hose showed promise but also flaws. When water flow was light, debris stalled on the slope and some water escaped capture, spilling over the edges. These hiccups didn’t deter the creator; they fueled a pivot to something bolder.
Meet the “Anacoanda,” a conical, spiral-shaped filter resembling a twisting channel that guides water downward while peeling it away from debris. The spiral design maximizes surface area, so more water gets captured even under heavy flow. Magnets embedded in the structure allow it to snap onto a downspout with ease and its modular design means you can flip it upside down to bypass filtration entirely. Testing showed this version outperforming its predecessors, with debris like sticks and leaves shooting out the bottom while clean water funneled into a collection pipe.
NeedItMakeIt is sharing the 3D print files for free on MakerWorld along with adapters for common downspout sizes 3×3 and 2×3 inches. The recommended materials are PETG or ASA for durability against the elements and off the shelf components like acrylic tubes and rectangular magnets keep costs low. A bit of silicone seals the seams to fix minor leaks from previous prototypes.
Of course there are still some issues, such as some pine needles and small sticks getting caught in the spiral. This means the taper might need to be adjusted for better debris ejection. As for germs in the microscopic cracks and microplastics leaching into the water, material selection and regular cleaning still need to be kept in mind. Thanks to the open source nature of the design, others can innovate further, maybe trying smoother surfaces or food grade filaments.
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