Toilet Flushing with Harvested Rainwater in Arizona

Using harvested rainwater for toilet flushing in Arizona is a practical way to reduce your water bill and conserve municipal supplies. With 13.6 inches of average annual rainfall, a 1,500-square-foot asphalt shingle roof in Arizona can collect approximately 8,373 gal per year. toilet flushing requires roughly 20 gallons per day per person, year-round. With this setup, rainwater can meet approximately 57.3% of your toilet flushing needs, saving an estimated $50.24 per year.

Annual Harvest 8,373 gal 1,500 sq ft roof
Annual Demand 14,600 gal toilet flushing (2 people)
Demand Met 57.3% of toilet flushing
Rec. Tank 500 gal storage capacity

Monthly Supply vs. Demand for Toilet Flushing in Arizona

The table below shows how your monthly rainwater harvest compares to toilet flushing demand throughout the year. Green values indicate months where your harvest exceeds demand (surplus water for tank storage), while red values show months where you will draw down your stored reserves. Toilet Flushing is a year-round use, so demand remains constant regardless of season. Tank sizing should bridge the gap during your driest months.

Month Harvest (gal) Demand (gal) Balance
January 673 1,240 -567
February 673 1,120 -447
March 673 1,240 -567
April 224 1,200 -976
May 150 1,240 -1,090
June 75 1,200 -1,125
July 1,121 1,240 -119
August 1,570 1,240 +330
September 1,121 1,200 -79
October 822 1,240 -418
November 523 1,200 -677
December 748 1,240 -492

Harvest by Roof Size for Toilet Flushing

A larger roof collection area directly increases your harvest and the percentage of toilet flushing demand you can meet with rainwater. The table below shows how different roof sizes perform in Arizona for toilet flushing (calculated for 2 people).

Roof Area Annual Harvest Demand Met Rec. Tank Savings/Year
1,000 sq ft 5,585 gal 38.3% 55 gal $33.51
1,500 sq ft 8,373 gal 57.3% 500 gal $50.24
2,000 sq ft 11,163 gal 76.5% 1,000 gal $66.98
2,500 sq ft 13,955 gal 95.6% 1,500 gal $83.73

Setting Up Rainwater Harvesting for Toilet Flushing in Arizona

Connecting rainwater to your toilets in Arizona requires a dedicated non-potable plumbing line (typically purple-colored pipe to distinguish it from potable supply). This is best planned during new construction or major renovation, though retrofit kits are available. The system includes a storage tank, submersible pump, pressure tank, sediment filter, and a backup connection to municipal water with an air gap to prevent cross-contamination. Most jurisdictions in Arizona require a plumbing permit for this type of installation. The payoff is substantial — toilet flushing accounts for roughly 30% of indoor water use, and switching to rainwater for this purpose provides year-round savings regardless of season. The recommended tank size for toilet flushing should bridge at least your driest month, ensuring continuous supply.

Metal Roof Upgrade: Toilet Flushing in Arizona

Upgrading to a metal roof increases your collection efficiency from 80% (asphalt shingle) to 95%, boosting your annual harvest to 9,944 gal from a 1,500-square-foot roof. This increases your toilet flushing demand coverage to 68.1% and raises annual savings to $59.66. Metal roofs also last 40-70 years compared to 20-30 years for asphalt shingle, and their smooth surface sheds debris more effectively, reducing maintenance on your collection system and improving water quality.

Other Uses for Rainwater in Arizona

Explore how harvested rainwater can serve other needs in Arizona:

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