System Q & A

1. Rainwater harvesting systems are a new invention in response to the recent droughts the US has been experiencing

Rainwater harvesting has been around for thousands of years. One resource can date rainwater harvesting tanks back to 2600 BC in India. Of course technology has advanced throughout the years and some of today's rainwater systems are very sophisticated systems.

2. Rainwater harvesting systems are nothing more than rain barrels connected to downspouts

The general population typically pictures a rain barrel when one mentions "rainwater harvesting." Rain barrels are great systems for small gardeners who prefer to hand water plants. However, rainwater systems can be utilized for much more than hand watering needs. Systems can supply water inside the home to wash clothes and flush toilets and some systems are even the sole household water source. Likewise, rainwater systems can be designed for commercial and even industrial needs and uses, including manufacturing processes, vehicle washing, laundry washing, etc.

3. Rainwater systems are only good when there is plentiful rain, not in times of drought

Drought is a shortage, but not the absence of rainfall. Rain will still fall during drought times and often it falls too hard for the ground to absorb and water is lost to surface runoff. Rainwater systems will collect nearly all the rainwater that falls on the collection surface (roof). This water can then be applied to the landscape at the appropriate rate that will allow the water to be absorbed in the ground.

Rainwater systems also allow for water storage to collect rainwater during wet seasons to reapply during dry seasons, which often is when water demand is highest. Rainwater can also be harvested even during the winter months when rain turns to snow. Snow covered roofs will melt and that water will be diverted to the rainwater storage tank to be stored for reuse.

4. Rainwater harvesting systems are highly complex systems that only a few professionals can install

Any licensed plumber can install rainwater harvesting systems. The components that make up a system are specific to rainwater harvesting, but the components follow basic plumbing guidelines. Any plumber that is well versed in float switches and pumps would be able to install a rainwater system.
Likewise, any septic system installer could install the tank with ease.

5. Rainwater contains many contaminants that are harmful to humans and animals

Properly designed systems can generate healthy water supplies. Having a first flush filter will assist in removing any potentially harmful organisms from the water storage tank. It is of utmost importance to have a first flush filter that does not clog, fail or harbor contaminants to protect the water quality. The stainless steel removable filter dries out between rain event, which prevents microbial growth and potentially contaminating the water supply.

Roof surfaces will have an impact on water quality. Metals roofs are ideal for rainwater systems and asphalt roofs should never be used. Copper roofing material should never be used either as it introduces unsafe copper levels into the environment.

Water entering a tank should be calmed to prevent stirring of the tank and disturbing the biofilm, which naturally forms in tanks. Biofilms are a slimy layer that form on rainwater tank walls and floor. It is compromised of bacteria naturally occurring in soil and metals. The biofilm layer protects water quality as metals are absorbed in this layer. Since the biofilm is made up of living organisms, oxygen is released into the water, again maintaining water quality within the tank.

First flush filters are critical to tank health as well. Eliminating decomposing organic material like leaves, sticks, and dead animals will prevent anaerobic conditions from forming in the tank, which would degrade the tank water quality and even contaminate the water.

6. Rainwater does not need to be filtered if it is used for irrigation

Tank water quality should always be protected no matter howe the water will be used. Pre-filtering rainwater with a first flush filter will eliminate organic debris entering the tank. Lack of pre-filtering will allow sticks, leaves, dead animals, etc. to enter the tank and will cause anaerobic conditions, which results in cloudy, foul smelling water. Also, organic matter in the tank will require cleaning and will clog hoses and irrigation heads. Money saved from excluding a pre-filter will be spent eventually for maintenance and may even cost more money than initially saved.

7. Rainwater harvesting tanks need to be emptied and disinfected every year to keep the water healthy

Properly designed rainwater harvesting systems require minimal maintenance - that includes never cleaning the tank. Due to the presence of beneficial biofilm in the tank, cleaning and disinfecting a tank would remove this beneficial layer. Tank cleaning should only be done if organic debris is allowed to enter the tank, which would result in anaerobic conditions with foul smelling and unhealthy water. Appropriate pre-tank filtering removes such organic debris to protect water quality and allow for the development of the beneficial biofilm layer.

8. Tanks should be large enough to store as much water as possible

Rainwater harvesting systems are not "one size fits all." The appropriate tank size depends on:

roof area
local rainfall
intended use

Tanks should be small enough to overflow regularly to provide skimming of the water surface, but large enough to provide a reliable water supply. One article covers the supply and demand balance to sizing the appropriate rainwater harvesting tank.

Typically, the largest expense in a rainwater harvesting system is the tank. Choosing the right tank size can make a difference in overall cost savings and investment payback.

9. Rainwater is another word for greywater

Misusing the term "greywater" for "rainwater" happens often, but the two are very different. Rainwater is the water that falls from the sky. Greywater is water that has already been used. An example of greywater is the water that has been used to wash clothes is collected and reused to irrigate a lawn or to flush a toilet. The treatment regulations for using rainwater and graywater are drastically different. Graywater can never be reused for drinking water. Rainwater, however, once it undergoes treatment (i.e. carbon filters and UV light treatment) can be consumed as drinking water.

In summation:
Rainwater is collected from a roof system and is used for washing clothes.
Greywater results from the clothes washing and is reused in the toilet.
Black water is the resulting water from toilet use and is diverted either to a water treatment system or to a septic system.