First-flush diverter plus UV sterilization

A two-stage system that first diverts the dirtiest roof water, then sterilizes what enters storage with ultraviolet light. This is the approach used in professional whole-house rainwater systems.

Stage 1: First-Flush Diverter

A first-flush diverter captures the initial 1-2 gallons of roof runoff per 1,000 sq ft of roof area. This first flush contains 90% of the bird droppings, dust, pollen, and debris. Commercial diverters ($30-50) install inline on the downspout and drain automatically between rain events.

Recommended: Rain Harvesting Pty First Flush Diverter (~$35-45).

Stage 2: UV Sterilization

UV-C light at 254nm destroys the DNA of bacteria, viruses, and protozoa. A UV sterilizer installs on the pipe between the storage tank and the point of use. Water passes through a chamber where a UV lamp irradiates it.

Recommended: Viqua VH200 (~$400-500) or SteriPEN Ultra (portable, $80-100 for small volumes).

Combined System Cost

• First-flush diverter: $35-50
• 5-micron sediment pre-filter: $30-50
• UV sterilizer: $400-500
• Total: $465-600 (plus storage tank)

Tips

• UV only works on clear water — turbid water shields pathogens from the UV light. Always pre-filter to at least 5 microns.
• Replace UV lamps annually (~$80-100) regardless of visible output — UV intensity degrades before the lamp visibly dims
• This system does not remove chemical contaminants — avoid collecting from asphalt-shingled roofs treated with zinc or copper