Wisy Vortex Filter for Pre-Filtering Your Rainwater Cistern System
Fixed Shipping to addresses in contiguous US
Features
This is one of our favorite pre-filters, used to filter the water immediately after it comes off the roof but before it enters the cistern. This filter is best used in ALL climates, is winter-proof, and is ideal for applications where more than 4 downspouts are being collected, on a roof under 2,200 square feet. With the vortex dynamic, the Wisy filter automatically diverts the first flush of water away from the cistern and then routes the remaining water into the tank through a vertically-mounted, stainless steel, cleanable filter screen. The filter screen also aerates the water as it passes through.
This filter can be installed in both above-ground and below-ground applications. For above-ground installations, a mounting bracket will be needed — you can build one from treated lumber, or purchase our stainless steel mounting bracket.
When installing underground, seal all joints (including the swivel joint) with the included sealant tape.
Ease of Installation: 8/10 when installing underground, 5/10 above-ground. The varying pipe elevations and potential for settling after installation make this a product best left to experienced installers. We recommend having some experience with running drainage piping.
Is This Right for You? If you have more than four downspouts and your property has some slope (this filter does not work on flat properties unless installed above-ground), this is a great choice. Note that the filter is not 100% efficient — expect approximately 70% of water to enter the cistern, with 30% carrying debris out through the bottom trash outlet. If this doesn't fit your situation, consider our other pre-filter options.
Frequency of Maintenance: Moderate. Pull the filter screen out and run it through the dishwasher, or scrub with dish soap and a soft-bristle brush. Start with monthly cleaning, then adjust based on your first year of use. High-pollen or heavily wooded areas may need more frequent cleaning; low-tree areas may only need cleaning every 6 months.
What Else Will I Need? If installing inground, consider adding the 20" riser — keep 4–6" above grade to prevent groundwater intrusion, and seal with silicone caulking or the included seal tape. You'll also need a short (~24") piece of 4" SDR-35 or 4" thinwall PVC pipe for the inlet bell and gasket. For the middle and bottom fittings, we recommend adding our 4" no-hub couplings to your order to adapt to 4" Schedule 40 PVC or 4" SDR-35.
Tools for Installation: A level, a shovel, silicone caulking, dish soap (to lubricate the pipe before inserting into the bell and gasket inlet), and something to compact the ground underneath the Wisy.
*For potable systems, additional filtration is required. This filter alone will not make rainwater potable.
Principles of Operation
The WISY WFF 100 Vortex Filter separates debris larger than 280 microns from collected rainwater and directs filtered water to the storage tank throughout an entire rain event — eliminating the need for any additional first-flush devices. Its diamond-cut vertical design delivers highly oxygenated water to the storage tank.
The WISY WFF 100 is the only commercial vertical filter of its kind and provides the highest quality of stored rainwater. The vertical design creates a self-cleaning effect: debris is discharged along with first-flush water through the bottom outlet, with no basket to clean and no additional sprayers required. The filter works on capillary action to deliver the highest quality stored rainwater with minimal maintenance.
Product Documents
For the WISY WFF 100 Vortex Filter spec sheet, click here.
For the WISY WFF 100 Vortex Filter installation manual, click here.
Visit our Design Library for free, commonly requested rainwater collection system plans — with itemized component price lists linked next to each design.
Wisy WFF 100 Vortex Filter — overview and installation walkthrough
Wisy WFF 100 Vortex Filter — video tutorial
Wisy WFF 100 Vortex Filter — installation detail
Wisy WFF 100 Vortex Filter — additional installation guidance
