Essentials of Rainwater Harvesting for Your Homestead

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Choosing the best rainwater harvesting system begins with figuring out your needs. What is the primary reason you want to capture water? Is it to have a backup water supply, to water vegetation, or to remove pooling water from your property?

From there, you can work with your budget to determine the size and best type of rainwater harvesting system for you. Consider your space, climate, and the quality of rainwater you expect.

Types of Rainwater Harvesting Systems

There are many solutions. Rainwater harvesting systems can usually be categorized as either passive or active types. There are also options that combine both.

  • Passive: Simple, eco-friendly solution
  • Active: High efficiency
  • Hybrid: Best of both

Passive systems:

  • Uses natural processes like gravity and percolation
  • Nothing mechanical to capture, convey, or treat rainwater
  • Simpler design
  • Cost-effective
  • Low maintenance

Passive systems often use landscaping elements like swales and rain gardens to manage water. Landscape type systems are usually considered passive and have the advantage of lower cost per volume of water.

Passive systems are generally more affordable and easier to integrate into your landscaping.

Active systems:

  • Uses mechanical and/or electrical means to capture, convey, and/or treat rainwater
  • Uses pumps, filters, and complex conveyance methods
  • Suited for large-scale operations
  • Better if you want higher water quality

Built type systems are usually considered active and have the advantage of providing cleaner water. Active systems might include storage tanks, water treatment, and distribution networks.

Active systems provide a more controlled and consistent water supply. For modern homesteads, the built type can be more reliable and have better water quality.


Most homesteads can take advantage of both types of systems or combine systems so the overflow of a built system becomes the source for a landscape system.

Finding the Best Rainwater Harvesting System for Your Situation

I often avoid using the terms passive versus active and instead refer to landscape versus built types. Landscape type systems of rainwater harvesting use landscape features to slow, absorb, and/or store rainwater.

Landscape type systems are usually considered passive. A built type system uses mechanical and/or electrical means to capture, convey, and/or treat rainwater.

Built type systems are usually considered active. Landscape types have the advantage of lower cost per volume of water. Built types have the advantage of providing cleaner water. For modern homestead, the built type offers some significant advantages.

Most homesteads can take advantage of both types of systems. Or even combining systems so that the overflow of a built system becomes the source for a landscape system.

Best Rainwater Harvesting System for Your Homestead
Best Rainwater Harvesting System for Your Homestead

Rainwater Harvesting Systems Components

Rainwater harvesting systems use various components to best meet needs. These components can be broken down into catchment surface, conveyance (gutters and downspouts), screens, first-flush, storage, water purification, and end use.

Catchment surface – Area that the rainwater falls on to be captured.

Conveyance (gutters and downspouts) – Transports the water from catchment to storage or use.

Screens – Separates debris from the water.

Pump – Pump to move water through the system to where it will be used.

First-flush – Diverts the first, and dirtiest, portion of rainwater.

Storage – Holds water for later use.

Water level indicator – Monitors the water level in the storage tank

Purification – Cleans the water to the needed level.

End use – Gives purpose to the system!

Rainwater Harvesting Systems Components
Before you decide which components you need, you should determine how much water you need, what you need it for, and how much you can catch.

Water Audit

You know your homestead better than anyone… often you can conduct a ‘water audit’ just on the back of an envelope. If you are using the water for drinking, you will need more treatment than if you are using it for gardens.

If you are using it for cleaning (tools, grounds, equipment, etc.), then you won’t need any treatment. It all depends on your needs and resources (e.g. do you only have seasonal need due to a seasonal creek).

Catchment Volume

The catchment volume is calculated from the precipitation falling on the collection area with some loss due to the efficiency of the collection materials (and leaks). In addition, conversion factors are used to yield the desired units of volume.

Typically, monthly catchment values are calculated based on monthly average precipitation data. The collection volume for any period of time is calculated using the following formula (mnemonic device Vrake):

Equation: Vrake – Rainwater harvesting potential.

V = Volume of collection in gal/time or m/time or liters/time

Note that time is usually in months. Use this to help determine potential yield and tank size.

R = Precipitation in inches/time or mm/time

Collect this data or find it from existing climate data.

A = Footprint of collection surface in ft2 or m2

This is the vertical projected area of the collection surface. For a rectangular house, use length times width.

k = Needed conversion factors, such as 7.48 gal/ft3 or easier SI units

Can also combine the 1ft/12in conversion for the precipitation data here.

e = Efficiency of collection surface (which is unitless)

75 soil, 0.8 average, 0.95 metal

Average rain harvested house roof
Many locations can collect sufficient water to meet needs. Often the limiting factor ends up being storage volume. Calculating monthly collection capacities minus monthly demand shows how much storage is needed.

Water Pressure

Another consideration is pressure. Pressure is critical to moving water from where it is gathered or stored to where it will be used. In a rainwater harvesting system, the water must be able to flow from catchment through the filters and conveyance into the first-flush and storage or end use.

This pressure can be provided by gravity from vertical height difference or by a pump. As an idea of how much pressure you will need:

Typical US residential water pressure is between 40 to 80 psi (pounds per square inch); typical drip irrigation systems (and some micro-sprinklers) need between 15 to 25 psi; and some appropriate technology drip irrigation systems need only 4 to 10 psi.

In addition to flow from catchment to storage, the flow from storage to end use is critical. Using the existing topography and/or platforms can often yield enough pressure for end use.

If necessary, a pump can be implemented to add sufficient pressure. While utilizing a pump increases the pressure, it also increases the upfront and operational costs.

Gravity acting on the vertical height of the water column is what produces the pressure, which is also referred to as head.

Make sure not to confuse volume with pressure (head). For instance, a 20-foot-tall water tower of 8000 gallons has the same water pressure as a 20-foot-tall pipe of 80 gallons.

If your homestead has varying topography, you want to catch and store the water at the high spots, and then use it in the low spots to provide enough pressure.

Otherwise a pump can be used to generate the needed pressure.

In a system we built in Eureka, California, we were able to change the existing local law to allow us to place the catchment tank where it made topological sense, without being restrained by set-back limits.

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The Book – To Catch The Rain

All of this and much more is included in a new book on Rainwater Harvesting, titled To Catch the Rain. All of the proceeds come back to the book and to the Appropedia Foundation (a non-profit).

Book To Catch The Rain

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