Have you considered rainwater harvesting for you home, but been held back by the prospect of “running out of water”? It’s a valid concern that is common among anyone considering collecting rainwater for their home use.
In this article, we unpack this question of “running out of water” and dive into the details of safeguards and calculations used to ensure water is always readily available.
When we started designing and installing rainwater harvesting systems in 2012, we decided that the only way that these would be valuable to people in the U.S. would be if they could still live like people in the U.S. Meaning, high-quality water, good water pressure, and a deep sense of security in knowing that they have as much water as they need.
That was our criteria for our systems.
- High-quality water
- Good pressure (Better than average)
- Sufficient water availability
Since then, every system we have designed and installed has met these conditions.
Local Rainfall Data
The first point to remediate this concern is 100-year rainfall data. That’s right. For every system we design and install, we pull historic rainfall data for that geographic region and use the data to create an average annual and monthly rainfall calculation.
Where we are in the southeast, rainfall occurs often enough to provide adequate rain supply for an average-size home. It rains about 50 inches per year in Knoxville, TN. We also work in Asheville, NC and Nashville, TN where it averages about the same 50 inches per year.
When designing a rainwater harvesting system, many homeowners have access to a secondary water source via municipal water or a well. We will often install an automatic crossover to that secondary source that automatically and seamlessly switches over to that secondary source in case of prolonged drought.
Fill ports come standard on all our systems. This allows for a tanker truck to easily deliver water and fill the rainwater tanks in case of prolonged drought. Local fire stations will generally deliver water for a small donation.
Chances of Running Out
During the design phase, calculations are made that show how many gallons of water the homeowner can expect to have at any given time during the year. In most cases, the water that is collected surpasses the estimated water demand the homeowner and their family would need.
Storage Size Calculation
The amount of storage used in a system design is a matter of efficiency. Too little storage and there won’t be enough reserve for between rainfall events. Too much storage and the homeowner will have simply paid for empty space that will rarely ever be filled with rainwater.
Now, there is a rainwater storage “sweet spot” and the homeowner can choose whether to be on the smaller or larger ends of that sweet spot. Thankfully, storage is often easy to add-on later down the road, especially in aboveground storage situations.
This is one of the most important data points to know if the homeowner will have sufficient water for the entire year – roof footprint. This isn’t the sq. ft. of the roof, but rather a measurement of how big the roof is from a top-down view. This will help us determine how much rain the roof can collect.
Family Size / Demand
How much water does the average person use every day? Does this family plan to use the water for heavy irrigation? What about livestock? Water usage calculations are very important.