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Rainwater harvesting is the collection, storage and distribution of rain water from the roof for use inside and outside the home, farm or business. Also known as cisterns.
Things to consider when determining the size of you storage tank include:
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.
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
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.
Daily indoor per capita water use in the typical single family home is 69.3 gallons.
Here is how it breaks down:
| Use | Gallons per Capita | Percentage of 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 | Gallons per Capita | Percentage of 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!
It is important to consider the space you have available and whether it will be placed above or below ground. In many cases tanks are installed above ground, especially when the tank is being installed along side an existing building.
Poly, metal, and bladder tanks can be installed above ground and are a popular option due to quick installation and low cost. Often incorporated as part of a new development for new homes, underground tanks are space saving solutions. Ideal for areas where the home is close to the property set back, slim line tanks can be utilized and are very attractive.
Popular due to their lightweight material, which makes for easy site preparation and installation, poly tanks are the most common for household use and come in a variety of shapes, sizes, and colors. Poly tanks are among the fastest growing types of tanks. They are made from polyethylene which is UV treated, impact modified and food grade, which means it is suitable for potable (drinking) water.
Metal tanks are extremely strong and many feature food grade polyethylene tank liners to prevent corrosion and ensure water quality. They have been popular for years and continued development of new colors, shapes, and sizes has ensured they still are.
Fiberglass tanks are corrosion resistant, sturdy and are relatively expensive but are long lasting. These tanks have been around for years and are made of the same material as boats.
New space saving bladder tanks have been developed in recent years. Bladder tanks are placed in crawl spaces or under homes with stem walls. They can store as little as 500 gallons and as much as 50,000 gallons, space permitting. They are sealed and flexible, and have extremely high puncture resistance. If space permits, multiple bladder tanks can be installed either end to end or side by side at opposite ends of a building. The possibilities are endless.
To get the pump that is best suited for your situation, it is best to talk to a professional. There are many factors that govern the type and size of the pump to deliver the water as you would expect.
It is the accessories that make the system. Having a tank that collects water without the proper accessories can be a constant maintenance issue. Be sure to get the proper accessories.
Please visit these websites for photos and detailed information about the rainwater harvesting options that are available to you.
