WHY WATER HARVEST?

  • Save money by reducing water bills.
  • Reduce demand on the municipal water supply.
  • Provide a water source during restrictions.
  • Make efficient use of a valuable resource.
  • Reduce flooding, erosion and the contamination of surface water with sediments, fertilizers and pesticides in rainfall run-off.

Rainwater quality is another benefit when compared to treated water sources. For example, naturally occurring rainwater is sodium-free, which can force salts away from the root zone, an important consideration in areas with waters with moderate to high salinity.

Many Texas cities offer rebates and tax exemptions for those willing to install a water harvesting system.

RAINFALL

Texas is particularly suitable for rainwater harvesting because of its unique rainfall pattern. Peak rainfall occurs in April and May, followed by a dry period from June to August, with more rain from September to October. Using an adequate rainwater harvesting system, Texans can easily get through the dry periods of the year without the need for additional water.

  • The Central Texas area receives an average of 32 inches of rain per year.
  • Walker County average annual rainfall is approximately 45 inches per year.

HOW MUCH DO YOU NEED?

The capacity of a rainwater harvesting system will depend on:

  • the amount of rainfall
  • the size of collection area
  • storage capacity
  • the household demand for water

To determine how much irrigation water is needed for outdoor uses of rainwater, consider:

  • types of plants selected
  • amount of exposure to direct summer sun
  • soil conditions
  • presence or lack of mulch
  • size of the area

The average household in Huntsville is about 4 inches/month.  A 2,000 square foot roof area could collect 4,000 gal/month.

If more than 4,000 gallons is used for irrigation each month consider increasing the size of storage in order to collect for the months when the rainfall is less than norm.

CATCHMENT SYSTEMS

Best catchments have hard, smooth surfaces (concrete, metal stone).

  • Roofs
  • Paved Areas
  • Soil

How much water can be collected?

  • One square foot of surface, receiving one inch of rain =  .62 gallons of water.
  • 1000 square foot of surface area x 1 inch of rain x 0.62 = 620 gallons

UP ON THE ROOF

How are you going to catch that rain?

  • To determine the square footage of catchment area of a house, use only the houses’ footprint.
  • The actual area of roof material will be greater due to the roof slope. (However, the amount of rainfall on the roof is not affected by the slope.)
  • The roof area will similarly receive 5.25 inches of rain which can be collected for irrigation purposes.
  • The 1,500 square feet of roof space will collect a total of 4,425 gallons of water.


Sample – Horizontal Catchment Area Size (Roof):

  • Section A (main house) is 60 feet wide x 25 feet          = 1,500 square feet
  • Section B (attached garage) is 20 feet wide x 25 feet  = 500 square feet
  • Total                                                                              = 2,000 square feet

Supply (gallons) = rainfall (inches) x 0.62 (conv) x catchment (area) x system (efficiency)
50″                     x 0.62               x  2,000 sq ft          x    0.8
= 49,600 gallons/year

Definitions:

  • Supply: The amount of rainfall we can collect (gallons).
  • Average Rainfall: Inches of rain per year.
  • Conversion: One horizontal square foot with water 1 inch deep is 0.62 gallons
  • Runoff Coefficient: The efficiency of the roof material allowing rainwater to runoff its surface.
  • System Efficiency: The efficiency of the system in capturing rainwater from roof, gutters, filters, tanks, etc..

DISTRIBUTION SYSTEMS

Are used to channel water from catchment systems to storage areas:

  • gutters
  • downspouts
  • sloped sidewalks
  • hillsides
  • streets and parking lot cutouts and channels
  • ditches
  • swales

STORAGE TANKS

storage tanks

1. Put storage near plants or at the end of downspouts
  • saves costs & work by reducing the amount of pipe and tubing needed
  • conserves water pressure by moving water a shorter distance

2. Elevate storage containers to take advantage of gravity flow

  • pressure increases with elevation by .43 psi per vertical foot
  • even a vertical change of 3 feet is enough to move water through a line
  • be sure to use low pressure valves
  • test the system before investing in a pump, it may not be needed

3. Hide unsightly containers in an unobtrusive place or behind a structure, screen and/or plants

  • because smaller cisterns are easy to handle and camouflage, place several of them near the irrigated site
  • for large landscaped areas, connect several tanks to increase storage capacity

4. If rainfall exceeds storage capacity, provide alternative storage for the exess or allow it to spill out.

  • Make sure storage container inlets and overflow outlets are the same size
  • Build concave planted areas to allow rainwater to percolate slowly into the soil, like a rain garden

Rainwater Project

water harvesting tank

The Walker County MG’s  developed a home-based rain collection system to provide irrigation for our Leaf-Pro Gardens.

Walker County Harvest Demo.pdf