6 Best Water Storage Tank Filters For Rainwater Collection That Prevent Algae
Keep your rainwater tank algae-free. Our guide reviews the top 6 filters that block the sunlight and sediment that cause growth, ensuring purer water.
Nothing is more satisfying than seeing your rainwater tanks fill up after a good downpour. But nothing is more frustrating than finding that water has turned into a green, soupy mess a few weeks later. Algae in your stored rainwater is more than just an eyesore; it clogs pumps, fouls irrigation lines, and can be harmful to livestock.
Disclosure: As an Amazon Associate, this site earns from qualifying purchases. Thank you!
Why Algae Blooms in Your Rainwater Tank
Algae isn’t some mystery that appears from nowhere. It’s a simple plant that needs three things to thrive: sunlight, water, and nutrients. Your tank provides the water, and unless it’s a completely opaque model, some sunlight will likely penetrate the plastic, giving algae the energy it needs to get started.
The real culprit, however, is the nutrient load. Every time it rains, the water washes everything off your roof and into your tank. This includes dust, pollen, bird droppings, and decomposing leaves. This organic cocktail is a five-star buffet for algae spores, giving them all the food they need to multiply and turn your precious water reserve into a science experiment.
Leaf Eater Advanced: Your First Line of Defense
Your filtration strategy should start before the water even enters the downpipe. A "leaf eater," also known as a rain head, is a non-negotiable first step. It’s essentially a screen that installs at the top of your downpipe, catching leaves, twigs, mosquitos, and other large debris before they have a chance to get into your system. Think of it as the bouncer at the front door.
This simple device does more than just keep sticks out of your pipes. By blocking that large organic matter, you’re cutting off a primary source of the nutrients algae feeds on. The less decomposing material that makes it into your tank, the less food there is for an algae bloom. This is the easiest and most impactful upgrade you can make to any rainwater harvesting system.
Rain Harvesting First Flush Water Diverter
The first few minutes of any rainfall are the dirtiest. This "first flush" washes away months of accumulated dust, pollen, and grime from your roof surface. A first flush diverter is a clever device that captures and redirects this initial, contaminated flow of water away from your tank, only allowing the cleaner water that follows to be collected.
Setting one up is straightforward. The diverter chamber fills with the first wave of dirty water, and once full, a ball seals the opening, sending the subsequent clean rainwater directly to your tank. After the rain, you simply drain the chamber to reset it for the next event. This single step dramatically reduces the amount of fine sediment and dissolved organic compounds—prime algae fuel—that reach your storage.
Rusco Spin-Down Filter for Visible Sediment
Even with a leaf eater and first flush diverter, fine sediment like sand, grit, and organic particles will make it into your tank. A spin-down filter is an excellent tool for capturing this visible gunk, typically installed on the outlet side of your tank before your pump. Water enters the filter and swirls in a vortex, slinging heavier particles to the outside where they collect in a clear bowl.
The beauty of a spin-down filter is its reusability. You don’t need to buy replacement cartridges. When you see sediment building up in the clear housing, you just open a small valve at the bottom to flush it out. This makes it a low-cost, low-maintenance option perfect for protecting pumps and irrigation emitters from grit without constant upkeep.
Pentek Big Blue Housing for Fine Filtration
For water that needs to be cleaner for specific uses, like washing equipment or for a workshop sink, a cartridge filter is the next logical step. The Pentek "Big Blue" is a common and reliable housing that accepts a wide range of filter cartridges. These filters are rated in microns, which is a measure of the particle size they can capture. A 20-micron filter will catch fine silt, while a 5-micron filter will remove most suspended particles, leaving your water visually crystal clear.
The tradeoff here is maintenance versus performance. The finer the filter (the lower the micron number), the more it will catch, but the faster it will clog. For general farm use, starting with a 20 or 50-micron sediment filter is a good balance. Remember, this filter’s job is to polish the water, not perform the heavy lifting—that’s what the pre-tank filters are for.
Viqua UV Sterilizer: Stopping Algae Growth
Sometimes, you need to be absolutely certain your water is biologically stable. A UV sterilizer doesn’t filter anything out; instead, it uses a powerful ultraviolet lamp to destroy the DNA of microorganisms like algae spores, bacteria, and viruses as the water flows past it. This is the ultimate solution for preventing algae growth at its source.
A UV system is an active sterilizer, meaning it requires electricity to run and the bulb needs to be replaced annually. It’s best installed as the very last step in your filtration chain, after all the sediment has been removed, to ensure the UV light can effectively reach and neutralize any living organisms. While it’s an investment, for anyone using rainwater for animal drinking troughs or applications where biological purity is critical, it provides unmatched peace of mind.
Water RINO Floating Intake: Draw Cleanest Water
This isn’t a filter, but a smarter way to pull water from your tank. Sediment and heavy organic matter sink to the bottom, while any oils or floating scum stay on the very top. The cleanest water in any tank is typically found about 6-8 inches below the surface. A floating intake, like the Water RINO, uses a float to keep the intake hose suspended in this clean water zone.
By drawing water from the cleanest part of the tank, you drastically reduce the amount of sediment and potential contaminants that your pump and downstream filters have to deal with. This extends the life of your filter cartridges, protects your pump from sludge, and ensures you’re always starting with the best quality water your tank has to offer. It’s a simple, brilliant concept that improves the performance of your entire system.
Maintaining Your Algae-Free Filtration System
A filtration system is not a "set it and forget it" appliance. It requires routine, but simple, maintenance to keep working effectively. A little bit of prevention saves you from having to deal with a 1,000-gallon tank of green sludge later on.
Make it a seasonal habit to check your system. After a big storm, clear the screen on your leaf eater. Once a month, drain your first flush diverter. Every few weeks, glance at your spin-down filter and flush it if needed. Keep an eye on your water pressure; a drop often means it’s time to change your cartridge filter. And if you have a UV sterilizer, mark your calendar to replace the bulb once a year. Consistent, small actions are what keep your water clear.
Preventing algae isn’t about finding one magic bullet filter. It’s about creating a layered system where each component handles a specific job, from blocking leaves at the gutter to sterilizing the water at the tap. By building your system thoughtfully, you protect your investment and ensure you have clean, reliable water when you need it most.
