Rainwater Harvesting: Benefits, Catchment Systems, Diverters & More

An Exhaustive Guide on Harvesting Water for a Green Home or Business.

Is Rainwater Acid?

Although acid rain in most areas is not considered a serious problem, rain becomes slightly acid as it falls because it dissolves carbon dioxide and nitrogen.

The pH or rainwater is about 5.7, whereas a pH of 7.0 is neutral. with the rain in Northeast Texas being the most acidic in the state.

However, with first-flush diverters, much or all of the acid-rain problems are solved.

If acidity is a problem, however, one tablespoon of baking soda per 100 gallons of water will neutralize the acid.

The Many Benefits of Rainwater

The benefits of rainwater harvesting are numerous:

  1. Reduces water bills.
  2. Plants thrive when irrigated with stored rainwater.
  3. As rainwater percolates into the soil, it forces salts down and away from root zones, allowing roots to grow better and making plants more drought tolerant.
  4. Reduces flow to storm sewers.
  5. Reduced water volume causes less erosion in urban areas.
  6. Helps municipalities meet summer water demand.
  7. Delays expansion of water treatment plants.
  8. Helps keep pesticides, fertilizers, and petroleum products out of groundwater and rivers.
  9. Distribution is easy and inexpensive.
  10. Can provide soft water for indoor non-potable use.
  11. Easy to expand.
  12. Reliable for irrigation, even in DFW.
  13. Pumps can run off solar energy or 12 volt systems.
  14. Water sources are renewable.
  15. Relatively inexpensive to install.
  16. Maintenance is easy and inexpensive.

Tax Benefits and Incentives for Renewable Water

Legislature in many areas has passed a number of bills and some local entities have adopted rules providing tax exemptions for rainwater harvesting systems.

Many legislatures allows taxing units of government the option to exempt from taxation all or part of the assessed value of a property on which water conservation modifications have been made.

Homeowners planning to install a rainwater harvesting system should check with their respective county appraisal district for guidance on exemptions from county property taxes.

Rainwater harvesting equipment at commercial installations is considered water-conserving equipment.

To qualify for the property tax exemption:

  • A facility must first receive a determination that the property is used for pollution control purposes,
  • The applicant then submits this use determination to the local tax appraisal district to obtain the property tax exemption.

Basics of Harvesting Rainwater

Rainwater harvesting is an alternative water supply and conservation approach that anyone can use.

A rainwater collection and storage system can be as simple as capturing rain in a barrel for gardening or complex enough to include input from such professionals as architects, engineers, rainwater specialists, and even water treatment specialists for potable water.

Implementing rainwater harvesting techniques directly benefits our municipalities by reducing demand on the water supply, and our planet by reducing run-off, erosion, and contamination of surface water.

Catchment of rainwater for outdoor use is quite simple, However, even landscape water needs care to reduce the amount of debris that will clog systems, feed warm weather algae blooms in the tanks, and increase maintenance.

A rainwater harvesting system consists of:

  • The supply or available rainfall.
  • The demand as water needed by plants.
  • A system for collecting water.
  • A system for moving it to the plants which can be as simple as using gravity or a complicated as using a pump to supply an irrigation system.

Simple systems distribute the rainwater immediately. Complex systems store some or all of the rainwater for later use.

Getting Started with a Rainwater Catchment System

The first step might be to design your landscape for native plants or other plants that have adapted well to your area. This should lower your needs for water and water storage.

There are some important criteria to consider for system, such as:

  • Size of collection surface–this is normally your roof.
  • Suitable location for storage tank or barrel..
  • Potential size of tank or barrel.

You also need to consider your area’s rainfall, including annual rainfall, normal dry period and the amount of water necessary for intended use.

Because the storage capacity needed should consider the potential collection capacity of your property, the storage requirements of your landscape, and the amount of rainfall in this area as well as the length of our dry spells, this is a good time to consult a professional for most homeowners.

Reuse Water with Rain Gardens

A rain garden is another way to renew water and turn storm water problems into landscaping assets.

It does this by slowing run-off and allowing water to soak into the ground.

Water is also cleaned by filtering through soil layers before it enters the groundwater system. Using plants in the rain garden accelerates soil drying between storms.

A rain garden is a depression that allows rainwater runoff from impervious urban areas like roofs, driveways, and sidewalks or from saturated soils an opportunity to infiltrate the soil and be “reused”. It is not a pond. but it is normally an artificial depression.

A rain garden requires an area where water can collect and infiltrate. Then simply adjusting the landscape so that water drains into this area may be all that is needed to establish a garden.

Native plants are recommended for rain gardens because they generally don’t require fertilizer and are more tolerant of local climate, soil, and water conditions. Plants must be chosen which can tolerate “wet roots.”

Plantings can also be planned to give year-round color to your landscape and provide a habitat for wildlife including birds, butterflies and other insects.

Because rain gardens are usually self sustaining, they can not only be designed for your individual yard but also be used as water conservation for an entire neighborhood or for a local park.

Rainwater Catchment System

Here is a basic diagram of a rainwater catchment system:

Functions of Rainwater Harvesting System

Collecting rainwater from impervious surfaces and storing it for later use, is a technique that has been used for millennia.

It has not been widely employed in industrialized societies that rely primarily on centralized water distribution systems, but with water resources drying up, rainwater catchment for irrigation can function as a major conservation tool to save potable water.

A rainwater harvesting system has six main functions–all within a design that fits your aesthetic requirements:

  • Collect as much rainwater as desirable or possible from your property.
  • Clean that water as is necessary for its intended use.
  • Convey that water to suitable storage.
  • Store the water.
  • Supply the water as intended.
  • Facilitate long term maintenance of the system.

Components of A Rainwater Harvesting System

Components of a rainwater system might include:

  • Catchment Surface
  • Gutters
  • Tank
  • Leaf Catcher
  • Access Cover
  • Downspouts
  • First Flush Diverter
  • Drain with Plug
  • Overflow Elbow
  • Spigot
  • Submersible Sump Pump

The Disadvantages of Rainwater Harvesting and Irrigation

Actually it was hard to find any disadvantages of this renewable water system. However, a few people may consider the following to be slight disadvantages of rainwater harvesting:

  1. Slightly more expensive than some other forms of landscape irrigation.
  2. Requires more maintenance than turning on a sprinkler system or hose.
  3. If tanks are large, may be aesthetically unappealing to some.
  4. Screening of tanks may cause problems with unreasonable homeowners’ associations.
  5. May not meet local building code requirements.

Downspouts in Rainwater Harvesting System

Downspouts convey water from the gutters to storage.

They should provide 1 square inch of opening for every 100 square feet of roof area. The maximum run of gutter for one downspout is 50 feet.

A good downspout is Schedule 40 PVC (or comparable) in a 4-inch diameter.
Other items of importance:

  • Use one- or two-way cleanouts in any horizontal pipe run exceeding 100 feet.
  • Do not exceed 45-degree angle bends in horizontal pipe runs.
  • Provide 1/4-inch slope per lineal foot minimum.

First-Flush Diverters

Although larger rooftop debris is collected by the leaf screens, smaller debris such as dust, insect bodies, animal feces, pesticides, etc., is not collected here.

A diverter takes care of the smaller debris.

The first flush diverter routes the initial flow of water from the harvest surface away from the storage tank.

A hose bibb fixture left slightly open (shown left as option ) or a pinhole drilled at the bottom of the pipe, allows water to gradually leak out. Water from the first-flush diverter be routed to a planted area if desired.

Pipe Diameter Needed to Catch Gallon of Water:

Diameter PVC PipeLength Per Gallon

Although not shown here, equipping the standpipe with ball valve is better. As the chamber fills, the ball floats up, traps the first-flush water, and routes the balance of the water to the tank.

How Much Water Should You Divert?

A rule of thumb is to divert a minimum of 10 gallons for every 1,000 square feet of collection surface.

However, opinions vary, and the correct answer will also depend upon the number of dry days dust has been allowed to accumulate, the amount and type of debris, the intensity of the rain (see below), the roof slope, and any tree overhang.

Even the season of the year can affect the amount of water to divert.

The rain intensity needed to wash your roof is a function of both the roof slope and the intensity of the rain.

  • Sloped Roof: Needs 0.10 inches of rain per hour.
  • Flat or Nearly-Flat Roof: Needs 0.18 inches of rain per hour.

A roof washer may also be needed for potable water or if you use the water for drip irrigation.

Once more: Particularly if you intend to use the harvesting system as drinking water, it is very important to consult a professional about your system.

Gutters in Rainwater Harvesting System

Gutters are installed to capture rainwater, normally off the roof of a building.

They should be installed with slope towards the downspout–slope should be 1/16 inch per lineal foot minimum

The side of the gutter closer to the building wall should be 1/2 inch higher than the side away from the building, This facilitates water draining away from the building.

There is no rule of thumb for gutter sizing because of such variables as:

  • Roof valleys
  • Steep slope of roof
  • Long roof distances from ridge to eave

Gutters should be made of inert materials. Many gutters are seamless aluminum installed by professionals.

You can also use half-round PVC, vinyl and galvanized steel but galvanized steel, copper, or aluminum are preferred gutter materials. Copper is a potential theft problem.

Gutters with lead solder which is often found on older gutters, should be replaced The slight acidity of rainwater might dissolve the lead into your harvested water.

When installing gutters, make certain that:

  1. There is a continuous slope to the downspouts.
  2. Nothing slows the flow of water and debris into the downspouts.

Areas where the water can pool collect insects, organic materials and bacteria–dangerous in potable water and undesirable in irrigation water.

Other problems with gutters are:

  • Inadequate number of downspouts.
  • Overrunning of water, particularly from roof valleys.
  • Inadequate gutter maintenance.

In addition to the gutters, you will need:

  • Drop outlet
  • Gutter hangers at 3 feet on center
  • Brackets
  • Straps
  • At least two 45-degree elbows to fit downspout pipe closely to the building side

Capacity for Tank Storage

Height (feet)6-foot Diameter12-foot Diameter18-foot Diameter

Economics of Rainwater Catchment

Rainwater harvesting systems can be as simple as a rain barrel for garden irrigation at the end of a downspout, or as complex as a domestic potable system or a multiple end-use system at a large corporate campus.

Rainwater harvesting is practical only when the volume and frequency of rainfall and size of the catchment surface can generate sufficient water for the intended purpose.

From a financial perspective, the installation and maintenance costs of a rainwater harvesting system for potable water cannot compete with water supplied by a central utility, but is often cost-competitive with installation of a well in rural settings.

Rainwater harvesting is practical for homeowners who are using the water for landscaping irrigation.

With adequate collection and storage capacity, it is an answer to water conservation for pools. It is not practical for those who supply their own potable water.

The Legalities of Renewable Water

The water that falls in your yard is legally yours. You can use it to water your yard or garden and, properly processed, even to shower or wash clothes.

With another processing step, admittedly probably too much for most of us, your legally-owned rainwater can be used for your family to drink.

However, once that water leaves your yard or property, you are no longer the legal owner of it. Hold on to that thought because it is going to be important to you in the future–probably the very near future.

Remember, rainwater is legally yours. You don’t want to lose it just as you might not want to lose the natural gas under your land.

In some parts of the United States, it is already illegal to add rainwater harvesting equipment to a property. Municipalities or states want or need it for drinking and agriculture.

Maybe that will never happen here. And maybe if it does, people who already harvest rainwater will be allowed to continue.

In the meantime, all you have to lose is money if you allow rainwater to leave your property unharvested and reused.

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