RAINWATER PRE-FILTRATION

Rainwater captured from rooftops contains significant quantities of plant debris, soil, eroded roof materials, and other solids that can clog pumps, valves, and pipes. Mineral solids collect as sediment at the bottom of storage tanks, reducing tank storage capacity. Organic solids remain in suspension and decompose, depleting oxygen and generating hydrogen sulfide and other noxious by-products.

One way to improve the quality of rainwater is to install a “roof washer” or “first-flush diverter”, a device that discards the initial runoff from a roof before it reaches the storage tank. While this technique has some value in regions with extended dry seasons and short but intense rain storms, It is not very effective in regions where rainfall is distributed throughout the year or where rain is often an all day event. Regardless of whether a first-flush diverter is installed, it is essential to filter all of the rainwater with low-maintenance, high-rate, mechanical filters specifically developed for rainwater harvesting. Because rainwater harvesting needs are so varied, we offer three first-flush diverters and nine mechanical filters.

FIRST-FLUSH DIVERTERS: A First-Flush Diverter retains the initial runoff from a roof in a length of pipe that is capped at the end. When the pipe is filled, a ball or flapper shuts off the top of the pipe so that additional rainfall flows directly into the rainwater storage tank. The pipe cap has a small-diameter outlet that slowly releases the “first-flush” water so that by the next rain the pipe is empty and is ready to receive more water. We offer three sizes that utilize 3”, 4”, and 12” pipe for water storage.

POT FILTERS: A Pot Filter is the simplest rainwater pre-filters, simply a flanged plastic tray with a perforated bottom that covers the top of a large basin with a side outlet. A filter pad is placed over the perforations, the pad is covered with gravel, and the outlet is piped to a rainwater tank. Water from a downspout dumps onto the gravel which strains out leaves and coarse debris and then flows through the filter mat which retains solid particles as small as 1/64”. With minimal maintenance, a pot filter can capture and filter 100% of the rainwater from a single residential downspout. Normally Pot Filters are buried so that the top is flush with the ground surface, but they can be used above ground.

BASKET FILTERS: A basket filter consists of a large screened filter basket that fits within a plastic filter body. Water flows in through a top port, down through the basket, and out through a bottom port. A second port is provided at the top to allow overflow should the filter basket become full. We offer two sizes designed for direct burial, our Small Basket Filter can filter 100% of the rainwater from roofs up to 5,000 square feet, and our Large Basket Filter can filter 100% of the rainwater from roofs up to 12,000 square feet. For both, the basket is easily accessible through a removable manhole cover, and the burial depth is adjustable with a telescopic extension.

small basket

filter
basket

Small Basket Filter
(5000 sq ft)

Large Basket Filter
(12,000 sq ft)

CASCADE FILTERS: In contrast with basket filters, Cascade Filters do not collect debris, but rather allow it to wash through the filter in order to minimize maintenance. This is achieved at the penalty of lower recovery rates, typically 95% depending on average rainfall intensity. Rainwater flows in through the top port and cascades over a curved, multi-level screened filter element positioned horizontally within a plastic filter body. Filtered water exits through one bottom port; debris is washed down the surface of the filter element and exits through a second bottom port.

We offer two sizes designed for direct burial, our Small Cascade Filter for roofs up to 5,000 square feet, and our Large Cascade Filter for roofs up to 16,000 square feet. For both, the filter element is easily accessible through a removable manhole cover, and the burial depth is adjustable with a telescopic extension.

We also offer an Internal Cascade Filter that fits completely within the access dome of some rainwater tanks, such as our Carat and DoubleTorus. This compact filter is suitable for roofs up to 5000 square feet.

small cascade element

cascade
filter element

Internal Cascade
Filter (5000 sq ft)

Small Cascade
Filter (5000 sq ft)

Large Cascade
Filter (16,000 sq ft)

VORTEX FILTERS: Like Cascade Filters, Vortex Filters do not collect debris, but rather allow it to wash through the filter in order to minimize maintenance. Instead of a horizontal fllter element, they utilize a vertical filter element. Rainwater flows in through the top port, spins around the circumference of the filter body, and spills into the top of the filter element. A capillary effect draws water through the side walls of the filter element and this filtered water exits through the upper side port. Debris washes down, passes through the open bottom of the filter element, and exits through the lower bottom port. This design requires very little maintenance, but at the penalty of reduced capture efficiency, typically 85% to 90% depending on average rainfall intensity.

We offer three sizes, a Small Vortex Filter for roofs up to 2,500 square feet, a Large Vortex Filter for roofs up to 5,000 square feet, and a Jumbo Vortex Filter for roofs up to 30,000 square feet. Each can be used above or below ground. When installed underground, the burial depth can be adjusted with an extension section, and the filter element is easily accessible through a removable manhole cover.

vortex element

vortex filter
element

Small Vortex Filter
(2500 sq ft)

Large Vortex Filter
(5000 sq ft)

Jumbo Vortex Filter
(30000 sq ft)

NOTE: In regions with long dry seasons followed by periods of intense rainfall, such as the American Southwest, we recommend reducing the maximum roof surface area listed for all filters by as much as 50%.

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