Are you considering supplying your entire house with rainwater? Properly sizing your rainwater harvesting tank is crucial for meeting your water needs efficiently. This guide will walk you through the key considerations and recommendations for determining the right tank size for your household based on average annual precipitation, monthly rainfall variation, and water usage.

Key Considerations:

• Average Annual Precipitation: This guide is tailored for areas with an average annual precipitation of 36 inches, evenly distributed throughout the year. This includes states like Ohio, Michigan, Indiana, Kentucky, West Virginia, Western Pennsylvania, Illinois, and much of the Midwest.
• Monthly Rainfall Variation: If your area's monthly rainfall varies significantly, calculate your tank size by multiplying your roof's square footage by 0.6, then by the highest monthly precipitation. For example, if May is the wettest month with 2.5 inches of rain, multiply by 2.5.
• Water Use: This guide assumes minimal irrigation use (e.g., occasional vegetable garden or house plants). If you plan to irrigate a lawn, you will need a significantly larger tank.

Sizing Recommendations:

Cabins with Occasional Use:

• Plastic Cistern: 1200-1700 gallons
• Concrete Cistern: 1000-2500 gallons
• Note: Ohio regulations require a minimum capacity of 2500 gallons for all rain cistern systems supplying a building/residence.

1-2 Person Household:

• Capacity: 2500-3000 gallons

3-5 Person Household:

• Capacity: 5500 gallons

6+ Person Household:

• Capacity: 8000-11000 gallons
• For most households, an 11000-gallon system is the maximum practical size unless you have several outbuildings or a very large house, assuming a Midwest U.S. climate.

Takeaway:

Determining the correct size for your rainwater harvesting tank involves considering your area's average annual precipitation, monthly rainfall variation, and your household's water usage. By following these guidelines, you can ensure that your rainwater harvesting system is appropriately sized to meet your needs, whether you have a small cabin or a large household. Proper planning and sizing will help you make the most of your rainwater harvesting efforts.