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Components of a Rainwater Harvesting System

This section is currently out of date. For up-to-date information, please see the RDN Rainwater Harvesting Guidebook

  1. The Roof
  2. Gutters
  3. Gutter Guard
  4. Downspouts
  5. Debris Traps
  6. Final Sediment Filtration
  7. First Flush Diverter
  8. Surge/Pump Tank
  9. Water Storage
  10. Water Disinfection
  11. Design & Maintenance

A rainwater collection and storage system is comprised of many components. To produce good quality water all of the components need to be considered together.

Rainwater collection systems can be roughly separated into two types - those where the water runs by gravity to the cistern and those where the water runs by gravity to a surge/pump tank and is then pumped to the cistern.

A gravity flow to the cistern (shown above) is ideal as it requires no power. Gravity flow to a surge tank and pumping to the cistern is a viable alternative where there is dependable hydro service or a back up battery/generator powered energy system.

Rain Harvesting Diagram


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The Roof

Metal Roof

Metal Roof

The key to choosing building materials for all parts of a rainwater harvesting system is to select materials that are non toxic and inert (non leaching.) This is particularly true of the roof that is subject to the oxidizing affects of sun and air borne pollutants. Avoid such contamination sources as lead flashings around sky lights or plumbing vents.

Torch on Membrane

Torch on Membrane

Water quality from different roof catchments is a function of the type of roof material, climate conditions, and surrounding environment. When choosing a roofing material - the smoother the better. The quantity of rainwater that can be collected is also a function of roof texture.

Metal Roof with Snow Guard

Metal Roof with Snow Guard

The most common type of roofing material used for rain catchment in British Columbia is galvanized metal that has been painted or enameled with a non-toxic material. Other materials include slate, terracotta tiles or concrete. Asphalt shingles are adequate but produce less water in summer and are harder to keep clean. Beware of the "modern" shingles that contain moss inhibitors if you plan to drink or bathe in the water.

Water collected from cedar roofs is acidic for plants and is impractical for indoor use.

Metal Roof with Snow Guard

Metal Roof with Snow Guard

Ashpalt Roof



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Gutters should be made of inert materials. The most common gutters are continuous, baked aluminum gutters made and installed on site. Half-round vinyl is also excellent.

Hidden Gutters

"Hidden gutters" are easy to clean.

Dirty Gutter

When installing gutters make sure that there is a continuous slope towards the downspouts, and that there is no impediment to slow the flow of debris into the downspouts. Areas where the water can pool collect insects, organic materials and bacteria. Think of a gutter as a river - not a wetlands or swamp.


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Gutter Guard

Gutter Guard

The decision to use gutter guard depends on the landscape and the number and type of shedding trees in the area. It keeps some debris out, but it also protects the debris that collects in the gutter, from the sanitizing and self cleaning of sun and wind.

Gutter Guard

In the Gulf Islands gutter guard is sometimes applied in the spring and fall to protect against arbutus berries, leaves and fir needlesl. The Rainwater Connection has done extensive research on different types of gutter guard and provides several choices.


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Anything from chains to traditional aluminum downspouts can be used to get the water down from the gutters.

Catchment Pipe

Sealed PVC piping is often used close to the ground, and where the water needs to be transported horizontally. This piping must be sized for good flows, storm events, and easy cleaning.


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Debris Traps

Debris Trap

The Rainwater Connection believes that a series of debris traps and filters and necessary to clean the water as much as possible before it enters storage. For agricultural water a small leaf trap and cleanable pipe systems to catch the larger heavier debris may be all that is required.


For potable water systems a series of leaf and debris traps are used as the first step - leaf traps to capture the leaves, needles and berries, and pipe "pigtails" collect the heavier black debris.

Hidden Debris Trap

The Rainwater Collection has developed several types of debris traps that work well in local conditions.

Debris Trap

The Rainwater Connection also uses some of the German and Australian equipment.


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Final Sediment Filtration

3080 Mesh Filters

For potable water systems the water is usually passed through some form of fine mesh screen filter as a final cleaning before entering the storage tank or cistern. These filters would clog up too fast if used on their own, but as part of a system they can significantly improve water quality and reduce cistern cleaning.

Mesh Filter

Gravity mesh screen versions are used in gravity systems, and can remove suspended particles as small as 150 microns. Even finer filtration can be achieved in a pumped system.


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First Flush Diverter

Box and Diverter

Flow past first flush diverter box
with valved dripper

The first flush diverter routes the first flow of water from the catchment surface away from the storage tank. It is designed to fill with contaminated water from a rain event and empty itself over a 24 hour period so that it is ready for the next time it rains This system is used in most parts of the world to improve water quality for potable water systems.

First Flush Diverter Buried

First flush diverter pipe,
buried in ground

First flush diverters ("FFD'S") have been shown to remove up to 80% of the pollutants that collect on the roof or in the gutters and become dissolved or suspended in the water. For example, it removes much of the discolouration and acidity from contact with cedar, arbutus and fir needle debris.

Buried First Flust Diverter Pipe

Buried first flush diverter pipe

The amount of water to reject depends on a variety of factors, including:

      • Roof and gutter slope
      • Roof material smoothness
      • Rain intensity
      • Preceding dry period
      • Airborne pollutants (dust, smoke, auto exhaust)
      • Tree debris
First Flush Diverter at Completion

Buried first flush diverter
pipe at completion

The rainwater Connection recommends rejecting at least the first 0.02 inch (0.5mm) of rain. This amounts to 10.4 imp gal per 1,000 sq ft of catchment area or 50 litres per 100m2. In extreme cases this is increased to as much as the first 0.04 or 1/25th inch.

The Rainwater Connection custom designs first flush diverters to suit individual circumstances. Most are simple flow past boxes or sloped pipes. Some of the Australian versions are also used.


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Surge/Pump Tank

Surge Pump Tank

Oil-free submersible pump

Where it is not possible or desirable for the roof water to run by gravity to the cistern it is directed to a surge/pump tank and is pumped to the cistern. The tank sizing depends on the roof size, the pump size and the desired storage capacity if/when the power fails.

It can be as small as 100 gallons and use a small oil free submersible pump or it can be over 500 -1000 gallons and the water can be pumped by a remote jet pump.

Catchement System

Catchment System Example

A simple wall hung catchment system with downspouts to all-in-one debris pails, down into the first flush diverter pipe (before backfill), and when the FFD pipe is full, through the gravity filter and into the 150 gal surge/pump tank. Note the surge tank overflow.


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Water Storage

Storage Cisterns

Water storage is the heart of a rainwater system in the Mediterranean climate of the Gulf islands and Vancouver Island.

Storage cisterns take many forms. As part of a design process it is important to assess your particular needs and the site opportunities to decide on the best option.

Polyethylene Tanks

The most common storage tanks are the above ground molded polyethylene tanks ranging in size from 300 to 3,000 gallons. These are the least expensive alternative, but offer relatively little protection from UV sunlight that can affect the quality of stored water.

Ensure good access for cleaning and avoid direct sunlight if possible.


Some polyethylene tanks can be partially buried to prevent sunlight penetration, or hidden under decks. Examples show below:

Buried Polyethylene Tanks
Polyethylene Tank Under Deck
Under-deck Polyethylene Tanks
Under-deck Polyethylene Tank
Culvert Steel Cistern

For larger applications, the Rainwater Connection supplies and installs steel polypropylene-lined cisterns 4,000-30,000 gallons that are made of culvert steel, structurally engineered, and easily transportable to most sites. The liner has a water potable rating. (NSF 61). These tanks can be partially buried, tucked away in the woods, or situated under decks.

Other storage options include in-ground concrete cisterns (shown below), and ponds.

Concrete Under Garage
Concrete Under House
Concrete Under Deck

20,000 gallon cistern under deck

Concrete Under Deck

20,000 gallon cistern under deck


Don't forget to consider winterizing measures and specialized fittings for emergency water exits that a pumper fire truck could hook up to.

Buried Winter Box
Buried Winter Box
Insulated Above-ground Box

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Water Disinfection

Water Disinfection Diagram

Treatment of rainwater is often simpler than treating water from wells or surface streams. Rainwater for indoor use requires a filtration and disinfection system to remove such things as parasites, bacteria, and virus from bird droppings, as well as insects, and wind blown materials that are carried onto the roof. Toxins leached from the roofing system can include heavy metals, petroleum products, algae, moulds, and yeast. (Note that many of these problems are also found in well water).

Filter and UV

A rainwater disinfection system can be as simple as particle filters and a UV light.


For added protection and water treatment a BioSand filter can be used. This type of passive sand filter uses very little water for its maintenance backflushing process.


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Good Design & Maintenance

is the Best Guarantee of Quality Water

Planning ahead and careful design of a rainwater harvesting system will improve water quality and save money in the long run - especially for new construction. The Rainwater Connection works closely with their clients to ensure a sensitive design that balances the need to:

      • Collect as much water as possible
      • Ensure good quality water
      • Facilitate long term maintenance
      • Fit the aesthetic requirements of the client

Rainwater harvesting systems require monthly and seasonal cleaning schedules to optimize water quality. The Rainwater Connection offers Owner's Manuals, 1st year monitoring of system, and annual maintenance contracts. Ease of operation and maintenance is designed into every system.

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