Overview
Believe it or not, rainwater can be filtered into some of the best-tasting, freshest water you've ever had. In our home state of Ohio, thousands of homes rely on rainwater as their sole water supply, and thousands more use it for the majority of their household needs.
But care must be taken. While rainwater is naturally purified through solar distillation, a lot can happen on the way back down — especially once it hits your roof and picks up organic material, debris, and animal waste. To return it to a safe, potable state, there are two proven approaches: a simple short-term method ideal for emergencies, and a full household filtration system for long-term use.
This article walks through both, with guidance drawn from a decade of hands-on rainwater system installations.
Filtration Methods
The Short-Term, Small-Scale Method
If you rely on a well pump (and the electricity to run it), or you're on municipal water and want an emergency backup, a short-term filtration solution is worth having on hand. We recommend pairing an ozone generator with your barrel or tank. Ozone (O3), when injected into a water supply, kills bacteria and algae quickly and then dissipates — leaving no residual effect on the water.
A few important notes: ozone will not remove harmful chemicals, so a water test is always recommended. Ozone should only be used outdoors, and the tank it serves should be in a well-ventilated area.
Full Household Rainwater Filtration
For a home system designed to supply drinking water, follow all of the steps below. It's tempting to skip one or two, but each step protects the others — cutting corners creates more maintenance work down the road. Here's the sequence we use in every drinking water installation:
- Pre-tank filtration: The first line of defense. We exclusively use Wisy Vortex pre-filters in all of our drinking water installations. These filters incorporate first-flush diversion and vertical filtration to prevent debris from entering your cistern — and they work so well that you'll rarely need to clean the tank. If you're looking to reduce upfront cost, at minimum consider an aluminum downspout debris filter to keep large debris out.
- In-tank filtration: Simple to implement and high-impact. Plumb your tank inlet so it turns 90° and runs down to just above the tank floor — this acts as a "force breaker" (also called a calming inlet) that reduces turbidity and keeps sediment settled. Draw water from the middle of the water column using a floating intake filter or a cistern pump to avoid the sediment-heavy top and bottom zones.
- Sediment filtration: Filter out remaining particulates before they reach your household plumbing. Sediment is measured in microns — the higher the number, the larger the particle. Ohio requires all drinking water systems to filter down to at least 5 microns (small enough to remove cysts). We install a two-stage system: a 20-micron filter first, followed by a 5-micron activated carbon block filter. Always install higher-micron elements before lower-micron ones.
- Activated carbon filtration: All water carries its own taste and odor — rainwater included. A granulated activated carbon (GAC) filter is essential for achieving the best possible water quality. We install a 5-micron carbon block cartridge immediately upstream of the UV sterilizer. You can choose between a simple cartridge-style GAC filter or a larger whole-house GAC unit depending on your system size.
- UV sterilization: The final and most critical step — disinfection. Even after filtering to 5 microns, bacteria can still be present. We prefer UV sterilization over chlorination because it leaves no chemical residue and delivers excellent water quality. UV lamp sleeves require cleaning roughly every 3 months to maintain full UV penetration, though with all the upstream filtration in place this is a quick job (under 5 minutes). Self-cleaning UV units are also available — our UV Pure units use a motorized wiper to keep the internal sleeve clear automatically. For more detail, see our article on UV Sterilization Systems.
Executive Summary
Rainwater can be a reliable, great-tasting drinking water source when properly filtered. For emergency or short-term use, an ozone generator is a simple and effective solution. For a full household system, follow this five-step sequence:
- Pre-tank filtration — Wisy Vortex filter or downspout debris screen
- In-tank design — calming inlet + floating intake to minimize turbidity
- Sediment filtration — 20-micron pre-filter followed by a 5-micron filter
- Activated carbon — GAC cartridge for taste, odor, and chemical removal
- UV sterilization — final disinfection step; no chemicals, excellent results
Each step protects the next. Skip one and you'll put extra burden on the rest of the system. Done right, a rainwater filtration system is low-maintenance, highly effective, and produces water that rivals — or beats — anything from the tap.
Questions about building your system? Browse our filtration products or reach out — we're happy to help design the right setup for your home.
