Tag Archives: first flush device

How To Keep Stored Rainwater Clean

fresh-839260_640Compared to surface water, rainwater is relatively clean to begin with. It is what rainwater comes in contact with that requires attention. Dust, pollen, organic materials, such as leaves and pine needles greatly affect the quality of stored rainwater.

Filtering out this debris upstream from storage should be included in your rainwater harvesting system. A high quality gutter screen is recommended as a first line of defense against debris, while it also keeps your gutters clean.

The use of downspout filters, or vortex filters, will improve the quality of your stored water by filtering and aerating rainWFF100-Vortex Filter_RainBankwater before it enters the storage tank. Removal of large particulate along with aeration greatly reduces the amount of harmful bacteria entering the storage tank. A downspout filter or vortex filter acts as first flush device and aerates the water and will not freeze as other first flush devices.

A smoothing inlet installed inside the bottom of the tank distributes the incoming water horizontally and prevents stirring up the sediments while aerating the water as it enters the tank. Aeration happens with each collection cycle and helps keep a healthy bio film at the bottom of the tank. There are beneficial microbes in the sediment that actually eat bacteria as they sink to the bottom. A healthily maintained bio film enhances the water quality in storage.

To prevent backup in the system during heavy rains, the storage tank should always include an overflow device. The overflow device allows water to overflow, but protects water quality in the storage tank with back flow prevention and vermin protection while also providing a skimming during overflow of buoyant debris, such as pollen, on the water surface.

Finally, a floating suction ensures the water being provided to the pressure pump and filtration is the cleanest water from the storage tank. Since all harvested rainwater is filtered before entering the tank, the floating filter should never clog, but will instead take water from just below the surface. Water at this depth is of the highest quality in the tank, because any particulate that enters the tank either floats on the surface or settles to the bottom. The floating filter acts as an uptake point for the pump than a filter; thus, the floating filter should never require maintenance.

RainBank Rainwater Systems is a dealer of Wisy and the Four Step System to ensure quality, collected rainwater.

Is Drinking Rainwater Bad for Us?

water-686917_640Although rainwater is generally considered clean, it can carry microbial and viral contamination generally caused by birds, rodents and insects. However, rainwater is relatively easy to filtrate and disinfect, resulting in improved quality over other drinking water supplies.

The Environmental Protection Agency (EPA) regulates the quality of public drinking water, but not private systems. The treatment of rainwater should be equal to that of surface water. All collected rainwater used for potable supply must be treated effectively to minimize risk of human health hazards. Contaminates need to be removed by filtration and sorption, or inactivated by disinfectant.

Both organic and inorganic contaminants need to be considered in design and installation of a rainwater collection system. Microbial and viral contamination in a rainwater collection system can be reduced by proper collection techniques such as screening, first flush devices, or vortex filters before storage. Environmental contaminants such as pesticides, fertilizers, and hydrocarbons should be considered, too. Raw water testing from the downspout at time of design will insure proper filtration in the treatment train, if needed.

Raw water should be tested to ensure that a RWC system is designed to produce high-quality potable water and tested after installation to be sure that the filtration and disinfection system is effectively removing any contaminants of concern.

To ensure that a RWC system is producing high-quality water, testing must be done. The EPA and local health agencies specify methods to analyze drinking water. Laboratories that conduct these tests are certified and governed by regulatory agencies. It is recommended that collected rainwater intended for single family domestic use be tested once per year for bacterial and any other constituents that are a concern.

How to Keep Collected Rainwater Clean

Gutter screening, first flush devices, vortex filters – which is best suited for my rainwater collection system?

Cottage without gutter screen
Without gutter screen

If you have been following my last few posts, you can start to understand the need to be sure that your collected rainwater is clean before it goes to storage. Keeping it clean will help keep tannins to a minimum, prevent debris from entering your cistern, and will also mean less demand on your filtration and disinfection systems.

With Gutter Screen
With gutter screen

Gutter screens are the first line of defense to keep your collected rainwater clean before storage. It is well worth the expense to purchase quality gutter screens to start with. Typically, an aluminum frame with stainless steel meshing works the best. They are expensive, but will make maintenance of your system much easier. Stay away from the low density foam insert types, they only clog up with debris and turn septic quickly. Light sheet metal type framing for screens tends to bow in the middle from the weight of the water. So spend some money up front and you won’t need to clean gutters.

A first flush device, or vortex filter is the second defense against debris from entering your rainwater system cisterns.

first flush device
First flush device

A first flush device is a vertical 3” or 4” vertical pipe that has a ball inside that will float to the top of the pipe as the initial water fills. When the ball gets to the top of the pipe, it closes off the vertical pipe and allows the water to move horizontally through a “t” and sends cleaner water to the cistern. The water at the cistern should go through a screen basket before entering the cistern for added protection.

vortex filterThe vortex filter is more of a hands-free device instead of the first flush and for most applications, this designer/installer prefers it. The vortex filter works on a centrifugal theory, where the water enters the top side of the filter from the tight line and is directed into a channeled side which swirls the water horizontally, passing through a screen, then towards storage. Residual water along with the debris falls through the center and towards waste. Only occasional cleaning of the screen is needed for maintenance, making this system as hands off as can be.

Things to consider when choosing a pre-screen system are:

  • Are my gutters hard to get at, are they second story?
  • Do I have a large amount of trees that shed needles and leaves to my roof or gutters?
  • Are my downspout lines connected to tight lines which convey water to the cisterns, or do they gravitate into the top of the cistern?
  • Am I willing and able to care for my first flush devices by maintaining their cleanliness?
  • Do I live in an area that is prone to sub-freezing temperatures?   

 If you have questions, or would like a specific topic covered, let me know in the comments.