Calculating the appropriate size
Rule number one!
Shoot for 1000 gallons and go from there. 1000 gallons on a 1000 to 3000 square foot house is a nice starting point and will supplement your existing water use quite nicely. Supplementing is the key word. It is not always practical to depend 100% on rainwater, but it is always practical to supplement potable water with rainwater.
Formulas:
square footage of roof area X .6 = gallons per 1 inch of rain.
gallons per 1 inch of rain X .average inches rain per month = amount available for collection
Example
Square footage of roof area (length x width) 1800 sq. ft
1800 x .6 = 1080 gallons
Average inches rain per month in most of Florida is 3 inches – this does not include June, July, August and September which are about double that.
1080 gallons x 3 = 3240 gallons collected
Let us assume 2 people live in this home. With each person using 69 gallons of water per day (this is average), that is 138 gallons per day or 966 gallons per week and 3864 gallons per month.
Considering the frequency of rain, a 1000 gallon to 2000 gallon storage capacity would be a good fit for this home.
Here’s how it breaks down:
Daily indoor per capita water use in the typical single family home is 69.3 gallons.
| Use | Gal per Capita | % Total Daily Use |
| Showers | 11.6 | 16.8% |
| Clothes Washers | 15.0 | 21.7% |
| Dishwashers | 1.0 | 1.4% |
| Toilets | 18.5 | 26.7% |
| Baths | 1.2 | 1.7% |
| Leaks | 9.5 | 13.7% |
| Faucets | 10.9 | 15.7% |
| Other Domestic Uses | 1.6 | 2.2% |
By installing more efficient water fixtures and regularly checking for leaks, households can reduce daily per capita water use by about 35% to about 45.2 gallons per day Here is how it breaks down for households using conservation measures:
| Use | Gal Per Capita | % Total Daily Use |
| Showers | 8.8 | 19.5% |
| Clothes Washers | 10.0 | 22.1% |
| Dishwashers | 0.7 | 1.5% |
| Toilets | 8.2 | 18.0% |
| Baths | 1.2 | 2.7% |
| Leaks | 4.0 | 8.8% |
| Faucets | 10.8 | 23.9% |
| Other Domestic Uses | 1.6 | 3.4% |
Considering the above figures, with efficient fixtures and a collection system capable of supplementing your water needs, you can make a significant impact on the environment and your pocketbook too!
What is rainwater harvesting?
Rainwater harvesting is the collection, storage and distribution of rainwater from the roof for use inside and outside the home, farm or business. Also known as cisterns.
Why we harvest rainwater.
- Increasing water usage as population continues to grow.
- Climate change.
- Storm water run off damages the environment.
- Increasing the storm water infrastructure cost taxpayers millions.
- Increase property value.
- Save potable water for drinking.
The Benefits are endless.
- Start harvesting water now! Rainwater reduces water usage in every home. Installing a system you will start saving water immediately.
- Rainwater is naturally pure and fresh. It is not recycled water!
- Research supports rainwater can meet all household requirements.
- Significant cost savings for the community and each household. When you consider the total cost to the community, it makes sense to install a system to catch rainwater that falls for free from the sky and utilize it in and around the home.
- Lower overall water usage. People that collect and use their own rainwater become more aware of their water use and further reduce their overall water use.
- Lower energy consumption and green house gas emissions. There are significant cost to treat and pump mains water throughout the community. Widespread installation of collection systems result in reduced energy consumption and less greenhouse gas emissions. Rainwater is an ideal water source for 95% of our requirements.
- Protect local waterways, bays, estuaries and reduce storm water infrastructure cost. Harvesting reduces both the volume and velocity of storm water run off.
