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Making the Most of Minimal Rainfall with Rainwater Harvesting: A Guide for Dryland Ecosystems

Updated: Mar 14, 2023

Water is one of the most precious resources on our planet, and unfortunately it is becoming increasingly scarce in many parts of the world. This is especially true in the dry climate here in Spokane, where we only average about 17 inches of rain each year. With climate change exacerbating drought conditions and population growth putting pressure on the water supply of our aquifer, it's more important than ever to find ways to conserve water. One solution is rainwater harvesting, which involves collecting and storing rainwater for later use.

Rain barrels and cisterns are two popular methods for rainwater harvesting. These simple yet effective systems can be used to collect and store rainwater from rooftops, driveways, and other surfaces. By using rain barrels and cisterns, homeowners can use a currently untapped resource and reduce their reliance on municipal water supplies.

In this article, we'll explore the benefits of rainwater harvesting and provide practical tips for collecting, storing, and using rainwater in your garden. We'll discuss the different types of rain barrels and cisterns available, as well as the factors to consider when choosing a location and size for your system. We'll also cover maintenance and upkeep, and highlight the many ways you can use rainwater to nourish your garden and its upkeep while conserving water.


Rain barrels and cisterns are two common types of rainwater harvesting systems used to collect and store rainwater for later use.

Rain barrels are typically smaller, above-ground containers that collect rainwater from rooftops, downspouts, and other surfaces. They are easy to install and maintain, and can be made from a variety of materials, such as plastic, wood, or metal. Rain barrels often come with a threaded spigot at the bottom for easy access to the collected water with any normal garden hose.

Cisterns, on the other hand, are larger, underground containers that can hold hundreds or thousands of gallons of water. They are usually made of concrete or plastic, and are designed to collect rainwater from larger roof areas or other surfaces. Cisterns require more planning and a more involved installation than rain barrels, but they can store significantly more water, making them a great option for larger properties.

Both rain barrels and cisterns are designed to capture rainwater and prevent it from running off into storm drains or other areas where it could cause damage. By using these systems to collect and store rainwater, homeowners can reduce their water bills, conserve water resources, and help protect the environment.


One of the first things people interested in harvesting rainwater want to know is how much water they can expect to collect. The amount of rainwater you can harvest depends on several factors, including the size of your roof and the amount of rainfall in your area. Let’s break down how to calculate how much rainwater you can harvest based on the square footage of your roof.

To begin, you'll need to measure the square footage of your roof. This can typically be done by measuring the length and width of your roof and multiplying those numbers together. For example, if your roof is 20 feet long and 30 feet wide, your square footage would be 600 square feet.

Once you have your square footage, you can use a simple formula to estimate how much rainwater you can harvest. This formula takes into account the average amount of rainfall in your area and the efficiency of your rainwater harvesting system. Here's the formula:


Let's break down each part of the formula:

  • Roof Area: This is the square footage of your roof, which we just calculated.

  • Rainfall: This is the average amount of rainfall in your area, typically measured in inches. In Spokane, our average is around 17.5 inches per year. If you don’t live in Spokane, you can find this information from your local weather station or online.

  • 0.62: This is a conversion factor that converts the area of your roof from square feet to gallons. For every 1” of rain and 1,000 square feet of impermeable surface (roof, driveway, etc), about 620 gallons are generated. Meaning, you can capture about .62 gallons per sq ft.

  • Harvesting Efficiency: This is the efficiency of your rainwater harvesting system. This can vary depending on the type of system you have and how well it's installed and maintained. A typical efficiency for a rain barrel or cistern system is around 80%.

Let's put the formula into action with an example. Say you have a 600 square foot roof and we use the average annual rainfall in the Spokane area of 17.5 inches. Using the formula, we can estimate the amount of rainwater you can harvest:

Rainwater Harvested (gallons) = 600 x 17.5 x 0.62 x 0.8 = 5,208 gallons

So in this example, you could potentially harvest over 5,000 gallons of rainwater per year!

Of course, this is just an estimate, and the actual amount of rainwater you collect will depend on many factors, including the size of your rain barrel or cistern, how often you empty it, and how much rainfall you receive in a given year (this does fluctuate year in and year out). However, this formula provides a good starting point for estimating the potential benefits of rainwater harvesting based on the square footage of your roof.


Collecting and storing rainwater is a simple and effective way to conserve water and reduce your water bill. Here's how to do it yourself:

  1. Choose your rain barrel or cistern. Consider the size and location of your property, the amount of rainfall you typically receive, and your budget when selecting your system. If you intend to use a cistern for rainwater harvesting, we recommend engaging a certified contractor who specializes in cistern installation as it typically requires excavation, permitting, and specialized tools.

  2. Install your system. Follow the manufacturer's instructions to install your rain barrel in a suitable location, ensuring the container is level and secure. Many homeowners will build a small platform for their rain barrel to keep it off the ground using cinder blocks or sturdy treated wood.

  3. Position your system under a downspout. Direct the downspout from your roof or gutter into your rain barrel.

  4. Use a filter. We recommend attaching a filter to your system to prevent leaves and debris from entering your container – this greatly reduces maintenance issues down the line.

  5. Maintain your system. Regularly clean your system and ensure it is free of debris. Empty your rain barrel before winter to prevent freezing and damage to the container.

By following these simple steps, you can collect and store rainwater for later use in your garden, reducing your reliance on municipal water supplies and promoting sustainability.


Rainwater is an excellent source of water for your garden because it is free of the chemicals found in tap water and has a somewhat neutral pH level, which is ideal for most plants. Here are some ways to use rainwater in your garden:

  1. Water your plants. Use a watering can or hose connected to your barrel to water your plants with the collected rainwater. This will provide them with the moisture they need to thrive.

  2. Wash your garden tools. Use rainwater to wash your garden tools and prevent the buildup of dirt and grime.

  3. Fill your pond or water feature. If you have a pond or water feature in your garden, use rainwater to fill it up. This will help maintain the natural balance of your water feature.

  4. Irrigate your lawn. Although we aren't proponents of a traditional green lawn, using rainwater harvesting can help it make more sense in our ecosystem (especially if you have an eco-lawn with a mix of grasses and clover!). Use a hose or sprinkler system to irrigate your lawn with the collected rainwater. This will help keep your grass healthy and green.

Using rainwater in your garden has many benefits, including reducing your water bill, conserving water resources, and promoting sustainable living. When using rainwater in your garden, it's important to note that it does not contain the minerals found in tap water, so you may need to supplement your plants (especially food crops) with additional nutrients. Overall, using rainwater in your garden is a great way to conserve water and promote a healthier, more sustainable environment.


Proper maintenance and upkeep of rain barrels and cisterns is crucial to ensure they function correctly and provide clean water for your household needs. Here are some tips to keep your rainwater collection system in top shape.

First, it's essential to clean the gutters and downspouts regularly. Leaves, twigs, and debris can accumulate in gutters and downspouts, causing water to overflow or clog the system. Cleaning them regularly prevents blockages and improves water flow.

Second, check and clean the screens and filters on your rain barrel or cistern. It's vital to prevent debris and pollutants from entering the system, which can contaminate the collected water.

Third, inspect the tank and fittings for cracks, leaks, or other damages regularly. Repair or replace damaged components promptly to prevent water loss and contamination.

Fourth, use a mosquito net to cover the opening of your rain barrel or cistern if you live in an area where mosquitoes are prevalent. This will prevent mosquitoes from breeding in the standing water and reduce the risk of mosquito-borne diseases.

Finally, flush the system periodically to remove any sediment, debris, or contaminants that may have accumulated in the tank or pipes. You can use the collected water for irrigation or other non-potable uses.

By following a regular maintenance schedule, you can ensure that your rainwater collection system provides clean water for your landscape’s needs and lasts for many years to come.


Collecting and using rainwater using rain barrels and cisterns is an effective way to conserve water resources and reduce our reliance on traditional water sources. By harvesting rainwater, we can make the most of the minimal rainfall we receive and promote a more sustainable environment. Moreover, the use of rainwater in our gardens and yards can benefit plant growth while reducing soil erosion and runoff.

Despite the numerous benefits of rainwater harvesting, it is important to note that the quality of the collected water is not suitable for human consumption. Do not drink harvested rainwater. Care must be taken to ensure the water is not contaminated with pollutants, debris, or toxic substances. It is also essential to maintain the rain barrel or cistern to avoid mosquito breeding or algae growth.

With proper installation, usage, and maintenance, rain barrels and cisterns can provide a valuable source of water for various purposes for many years. In the face of growing concerns over water resources and the impact of climate change, using rainwater is an essential step we can all take towards a more sustainable future.

In short, rain barrels and cisterns are a simple and effective way to collect and use rainwater, reduce our water usage, and promote a more sustainable environment. With these tools, we can make the most of minimal rainfall and contribute to a better future for ourselves and generations to come.


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