Toilet Flushing with Harvested Rainwater in Idaho

Using harvested rainwater for toilet flushing in Idaho is a practical way to reduce your water bill and conserve municipal supplies. With 18.9 inches of average annual rainfall, a 1,500-square-foot asphalt shingle roof in Idaho can collect approximately 11,514 gal per year. toilet flushing requires roughly 20 gallons per day per person, year-round. With this setup, rainwater can meet approximately 78.9% of your toilet flushing needs, saving an estimated $46.06 per year.

Annual Harvest 11,514 gal 1,500 sq ft roof
Annual Demand 14,600 gal toilet flushing (2 people)
Demand Met 78.9% of toilet flushing
Rec. Tank 275 gal storage capacity

Monthly Supply vs. Demand for Toilet Flushing in Idaho

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 1,346 1,240 +106
February 972 1,120 -148
March 1,121 1,240 -119
April 1,047 1,200 -153
May 1,196 1,240 -44
June 897 1,200 -303
July 374 1,240 -866
August 374 1,240 -866
September 598 1,200 -602
October 748 1,240 -492
November 1,346 1,200 +146
December 1,495 1,240 +255

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 Idaho for toilet flushing (calculated for 2 people).

Roof Area Annual Harvest Demand Met Rec. Tank Savings/Year
1,000 sq ft 7,675 gal 52.6% 55 gal $30.70
1,500 sq ft 11,514 gal 78.9% 275 gal $46.06
2,000 sq ft 15,350 gal 100.0% 1,000 gal $58.40
2,500 sq ft 19,189 gal 100.0% 1,500 gal $58.40

Setting Up Rainwater Harvesting for Toilet Flushing in Idaho

Connecting rainwater to your toilets in Idaho 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 Idaho 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 Idaho

Upgrading to a metal roof increases your collection efficiency from 80% (asphalt shingle) to 95%, boosting your annual harvest to 13,672 gal from a 1,500-square-foot roof. This increases your toilet flushing demand coverage to 93.6% and raises annual savings to $54.69. 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 Idaho

Explore how harvested rainwater can serve other needs in Idaho:

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Use our Rainwater Harvesting Calculator to enter your exact roof area, material, and combine multiple uses for a comprehensive harvest analysis. See all rainwater harvesting data for Idaho or compare all 50 states.