Very simply, rainwater harvesting systems are comprised of the following:

1. Collection

2. Treatment

3. Storage

4. Distribution

Collection of rainwater and other condensation sources such as air conditioning units is the first step in the process.  This consists of a simple array of piping, troughs or ducts to collect the water sources and direct them to a storage tank, reservoir or cistern.  As the water enters the storage, it is filtered to remove debris.

Bag filters are often used here due to their high capacity, simplicity and low operating costs.

 Bag Filters

Treatment of the water begins with filtration typically in the 5 micron range.  From there, the water undergoes disinfection to eliminate microbiological substances such as bacteria, viruses and cysts.
 

Cartridge filters are the usual choice here. They can reliably remove minute particles and they occupy less space than bag filters for the same flow rate.

Cartridge Filters

Filter Housings

Disinfection methods can range from chemicals such as sodium hypochlorite or chlorine dioxide (both generated on site) to a chemical-free alternative such as ultraviolet (UV) light.  For small systems, UV light may be the only disinfection step.  A combination of chemical disinfection and UV disinfection are employed for larger systems.

UV Light Systems

On-Site Hypochlorite Generation Systems

Chlorine Dioxide Generation Systems

Depending on the source of the collected water, the pH or alkalinity of the water may need adjustment to prevent corrosion of the existing plumbing system and fixtures.  For this, a small chemical feed system is used to dose the appropriate chemical(s) to bring the water quality into alignment.  In some cases, a dye is added to the reclaimed water so that it is easily identified as being a non-potable source.

Chemical Feed Systems

Treatment systems must also include on line measurement and control ensuring safe, reliable and cost effective operation.  Even though the reclaimed water will not be used for potable applications, there is still a level of quality that must be maintained for safety and to meet regulatory guidelines.  In addition, precise measurement and control will ensure the lowest possible operating costs, reducing excess chemical and energy consumption.

Strantrol® 890 Controller
More Analyzers and Controllers

Storage of the treated water involves provisions for introduction of potable water to maintain the volume required for the demand.  As described earlier, reclaimed water will only reduce the amount of potable water for non-potable applications, not eliminate it.

For large storage tanks, it is common to circulate treated water through the storage tank and the disinfection system to maintain the desired level of residual disinfectant.  For smaller storage tanks, circulation is not necessary.

Distribution of the reclaimed water is the last step of the process.  Pumps deliver the water, through dedicated piping and plumbing, to the bathroom fixtures, laundry or irrigation system.  In some cases, UV light is used as a final disinfection step as the water is pumped from the storage tank for added safety.

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