Rainwater Harvesting

Introduction: This is a primer for setting up a rainwater harvesting system. Many in-depth manuals are available regarding the actual construction of the systems. State regulations need to be consulted as well, as some states require certain types of water storage containers. Ohio, Kentucky, Hawaii, Arizona, New Mexico, Washington, West Virginia, Texas, and the U.S. Virgin Islands are considering or have developed rules related to rainwater harvesting.

Here are some examples of rainwater collection systems from different times and from around the world.

Benefits: (just a few)

RainWater is Free
Secondary water source or backup if city/well water is contaminated
Neutral pH is better for irrigation
Softness keeps appliances working better
Rainwater is sodium free
Reduced utility bills
No harmful natural or man-made toxins

Overview of Rainwater Harvesting Components:

Catchment surface: the collection surface from which rainfall runs off
Gutters and downspouts: channel water from the roof to the tank
Leaf screens, first-flush diverters, and roof washers: components which remove debris and dust from the captured rainwater before it goes to the tank
One or more storage tanks, also called cisterns
Delivery system: gravity-fed or pumped to the end use
Treatment/purification: for potable systems, filters and other methods to make the water safe to drink

Roof types:

Metal, specifically trade name Galvalume, is the best as it’s slick texture is great for efficiency and the water is absorbing harmful chemicals
Clay and concrete tile are very porous leading to greater loss due to evaporation and inefficient flow
Composite or asphalt shingle can be used for irrigation only as the rainwater absorbs too many toxins to be used for potable systems
Wood shingle, tar, and gravel are also only to be used for non-potable systems
Slate’s smoothness makes it ideal for a catchment surface for potable use, assuming no toxic sealant is used

Gutters:

The best gutter types are half-round PVC, vinyl, pipe, seamless aluminum and galvanized steel
No lead solder should be used in gutters as they can leech into the water supply
Ensure leaf screens are installed to take out the large contaminates

Gutter types and costs table

First-Flush Diverter should be installed next in order to separate the leaves, dust, and bird droppings from your water to be stored. This water can be stored in a separate 55 gal drum for irrigation if desired.

First Flush

For potable rainwater harvesting systems, the next step will be a smaller pre-storage filter (or Roof Washer) of approximately 30 micron. These will need to be cleaned often to ensure proper flow and so that the filter itself does not become a breeding ground for pathogens.
Roof Washer types and costs table

Storage tanks:

Must be opaque to inhibit algae growth
Must never have been used to store toxic materials
Must be covered and vents screened to discourage mosquito breeding
Must be accessible for cleaning
Can be made from fiberglass, polypropylene, wood, metal, ferrocement, and concrete

Storage tank types and costs table

Water pressure:

Standard city water pressure is 40-60 psi
Home appliances generally require 20-30 psi
For gravity flow water gains 1 psi for every 2.31 feet of vertical rise
Pumps are designed to push not pull the water so they should be situated close to the source

Water Pressure systems and costs table

Filtration: The most popular disinfection array is two in-line sediment filters consisting of a 5-micron fiber cartridge followed by a 3-micron activated charcoal cartridge filter, and those followed by an ultraviolet light. This system is placed just after the pump.
Water filtration systems and costs table

Estimating usage:
A helpful table to estimate water usage
Sample rainwater harvesting balance worksheet

Costs: From a financial perspective, the installation and maintenance costs of a 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.

Storage tanks are the most expensive component of rainwater harvesting.

Another helpful table:

Water Treatment Techniques Table