Summary of treatment practices used in stormwater harvest and use systems
Link to this table

Treatment Method Primary Purpose Location in System
Pre-storage and in-storage treatment
Filtration/Biofiltration Reduce particulates and nutrients Before storage
Grassed Swale Reduce particulates Before sedimentation
Leaf Screens and Strainers1 Remove organic solids Gutters and downspouts (before sedimentation)
Vortex Filters Remove organic and gross solids, particulates and debris down to 280 microns. Before storage and connected to smoothing inlet in tank.
Screens Reduce gross solids Before sedimentation
Settling Basin/Sedimentation1 Remove particulates Before or during storage
Smoothing Inlet Prevents the resuspension of settled solids and introduces oxygen to the tank to enhance aerobic conditions In tank
Floating Filter Filter particulates before water enters a submersible pump (protects pump) In tank
Skimming Overflow Siphon and Trap Remove floating debris, (e.g. pollen) and creates a water trap to prevent animals and downstream odors from entering the tank. In tank
Aeration Unit Used to introduce oxygen to tank which aids in the formation of aerobic beneficial bacteria that have been shown to reduce nutrient and metals concentrations. In tank or can be set up in a venture injection application.
Post-storage treatment
Activated Charcoal1 Remove chlorine, reduce odor, remove organics After sediment filtration, before use and before or after UV filter
Boiling/distilling1 Kill microorganisms Before use
Chemical treatments (chlorine) 1, a Kill microorganisms During storage or at distribution. Most commonly injected post filtration at point of distribution or in day tank. Should not be required in tank if adequate prefiltration is implemented
Electrodialysis2 Remove dissolved ions (salts) Between storage and end use

Not required in rainwater systems

In-line filters Removes sediment, reduces turbidity, increases ultraviolet treatment Between storage and end use and prior to UV treatment. Recommend 1 micron to meet current indoor water quality criteria of less than 1 ntu or sample the water and send to the UV manufacturer.
Microfiltration2 Remove suspended solids and microorganisms Between storage and end use
Ultrafiltration Remove suspended solids,organics Between storage and end use
Nano-filtration2 Remove multivalent ions, organics microorganisms, viruses and proteins Between storage and end use
Reverse Osmosis2 Remove monovalent ions, organics, microorganisms and viruses. May remove beneficial nutrients and produce highly corrosive water that needs to be reconditioned. Between storage and end use
Sand filtration Between storage and end use
Ozonizationb Inactivate microorganisms Before use typically applied through a venture and injected into the tank or a smaller contact tank.
Ultraviolet Disinfectionb Inactivate microorganisms Before use

1Georgia DCA, 2009
2Met Council, 2011
aBefore activated charcoal (if included)
bAfter activated charcoal (if included). Refer to specific UV and carbon filter manufacturer for guidance,br> 3 VA Rainwater Harvesting Manual, Cabell Brand center, 2009

This page was last edited on 16 April 2020, at 18:03.