A Quick List of Filters Used in Residential Rainwater Collection

 

While a filter is not a requirement on most rainwater collection systems, there are instances where filters are either desired or required. 

In a basic rainwater collection system, water moves from the roof to the gutters then down the downspout and into a cistern (rain barrel) where it is stored for later use. A spigot is affixed to the cistern to access and use the stored water by either filling a watering can or connecting a hose to transport water to plants around the garden. With proper design and installation this original, basic setup can achieve great results for many, many years without the need for service. Even today, we still recommend that most people start with this basic rainwater collection system.

 

Rainwater is naturally distilled and considered “pure”

The use of filters in rainwater harvesting systems depends on both site conditions (roof type, surrounding environment) and end use (gravity feed vs. micro-irrigation, potable vs. non-potable).  Rainwater is naturally distilled and considered “pure” when it lands on our rooftops (https://www.waterwisefl.com/a-simple-trick/).  However, contaminants such as leaves, bird droppings, dust, dirt, and loose roofing materials can be picked up as the water travels over rooftops, through gutters or into storage tanks.

Filters are used at various stages of a rainwater collection system.

Every filter ultimately serves to trap debris, both large and small.  Pre-filters are installed ahead of the storage tank and primarily filter large debris while post-filters are installed after or in the storage tank to filter out smaller debris.  If a dedicated filter is not installed, debris will settle in the bottom of the cistern, essentially making the cistern the filter.  Filters can be used exclusively, but are much more effective when used in combination.

This article will look at the different filter types that we have installed, offer pros and cons of each and touch on which applications each filter is best used for.

Let’s take it from the top……..literally.

The best way to keep a system clean is to stop any debris from ever entering the system. This starts at the top and involves mesh screens catching larger debris while still allowing water to flow through. These pre-filters can be installed on top of the gutter, the top of the downspout, in the downspout, or on top of the cistern itself.  With mesh screens, you often get what you pay for.

Gutter screens (or gutter guards) are the first line of defense.  These mesh screens are installed on top of the gutter to allow water to enter the gutter but keeps out most of the leaves and other debris (see picture 1).  Prices vary ($0.10 to $2 a foot) and these filters can be found in most home-improvement stores and are easy to install.  Furthermore, they are self-cleaning as debris simply washes off the top of the screen.  Gutter screens are a must in gutter sections where leafy trees hang over a roof.

Mesh Gutter Screen

Picture 1: Mesh gutter screens

Located within the gutter at the top opening of the downspout, a downspout leaf strainer acts as a colander to block leaves and large debris from entering the downspout.  These devices which look like a small, metal hairnet (think: lunch lady) are very inexpensive and readily available (Picture 2).  While effective at stopping debris, the major downside here is maintenance as leaf strainers must be cleaned out often, usually by hand.  A clogged leaf strainer prevents water from entering the downspout resulting in a messy overflow pouring out of your gutters and no water in your cistern.

Gutter Strainer

Picture 2:  Downspout leaf strainer

A filter placed within the downspout (leaf catcher or leaf eater) is a great choice for a hands-off, long term solution (Picture 3).  Water and debris passes through the gutter and downspout, but gets caught in the downspout in-line filter.  The downspout filter collects debris at one point to make for easy maintenance.  If the leaf collector is not self-cleaning, it often only requires that a tray is pulled out and dumped.  The downside here is installation as a section of gutter needs to be removed to accommodate the new filter.  The cost of the downspout filter itself plus the added installation costs will increase the overall cost of your system. Some downspout filters also act as a diverter to both filter water and move to the storage tank while controlling overflow.

Downspout Filter

Picture 3: Self-cleaning downspout filter (image source: http://www.aquabarrel.com/product_list.php)

Another type of mesh screen can be placed at the inlet of the cistern, often on top of the storage tank (see Picture 4).  This is a large screen or filter basket that collects debris after the downspout and just before entering the barrel.  The inlet screen is inexpensive; however, it requires a large, expensive hole saw to get that perfect cut and fit.  A jigsaw can also be used to make the cut but the slightest error will leave gaps that allow mosquitos can enter.  These filters are somewhat self-cleaning as the inlet screen does not become clogged, but a lot of debris may accumulate on top of the barrel.  It is important to note that the inlet hole for this type of filter will be very large, and therefore the outlet hole must be very large too.  If the inlet size is greater than the overflow outlet size, you will have overflow at the barrel and a flooded mess on a big rain event.

Filter Basket

Picture 4:  Mesh cistern screen in action

Also located with the downspout is the first-flush diverter (picture 5).  The general idea behind the first flush is that significant debris (dirt, dust, bird droppings, leaves, etc.) can buildup on a roof between rain events.  Once the rain finally hits, the dirt is washed off the roof with the first flush of water to a pipe located ahead of the storage tank where it collects and slowly percolates out.  When the first flush pipe reaches capacity, a float ball closes the reservoir and diverts the water to the catchment system.  First flush systems are an effective way to keep dirt and contaminants out of your storage tank, but product and installation costs are high.

First Flush

Picture 5: First flush filter system

Now that we have filtered out the big stuff, the water in the cistern can be accessed at the spigot with the help gravity to fill watering cans and move water out to different areas of the yard using hoses.  Rainwater that will be used in irrigation systems will require the addition of post-filters to remove the smaller pieces of debris that can clog the irrigation system.  Small particle filtration can be accomplished at the pump itself or in the irrigation line before reaching the emitters.

Most pumps have a sediment filter included in the body of the pump.  However, using only the filter that comes in the pump will lead to more maintenance as the pump’s filter will need to be cleaned frequently. Don’t do it.   A dirty pump filter will not move water through the irrigation system effectively and can even damage the pump.  Placing the pump inside a filter bag is a simple fix.  Inexpensive and highly effective, filter bags greatly reduce the amount of maintenance as they are essentially a filter for the pump filter and are somewhat self-cleaning (see Picture 6).

Filter Bag

Picture 6:  Pump filter bag

A fourth filter type is installed in irrigation system line after the cistern and spigot.  This filter type is usually the last line of defense to combat debris entering and clogging your irrigation tubing and emitters.  An in-line filter (also called y-filter due to their shape) can remove extremely small, microscopic debris (at the micron level) but must be used in conjunction with a filter from above that removes the larger debris (see Picture 7).  Although inexpensive, in-line filters need to be cleaned out periodically.  Simply unscrew the filter cartridge and hit the filter with a high-pressure hose.

Y Filter

Picture 7: In-line micro-irrigation filter, y-filter

There you have it – a quick rundown of some rain water harvesting filters.  This list is by no means conclusive as there are more filters out there and new products continue to hit the market.  For the greatest effect, it is best to use filter in combination to eliminate both the larger then smaller particulates.  First flush systems can and should be used as an additional third layer when the roof catchment area is severely in question.  If your final use of the rainwater you collect is for consumption, you will need to add additional filters – primarily a multi-stage system with an ultraviolet light sanitizer – to make the water potable.

 

We hope that you find our experiences with various filters useful in designing your rain barrel system.  Please contact us directly for a full-service design and installation. We take the guesswork and time out of your way so you can start to enjoy the benefits of having an unlimited source of pure water at your disposal. Your plants will thank you!