Water Reuse

Feasible Non-Potable Uses and Limitations

While potable use is effectively off the table, using rainwater for non-potable purposes is a realistic option, though it still comes with significant regulations.

• Allowed Uses: The most common and allowable uses for rainwater at a school would be:

  • Subsurface landscape irrigation (watering playing fields, gardens).

  • Toilet and urinal flushing.

• Dual Piping: The school would need a completely separate, purple-colored piping system for the non-potable rainwater to ensure it never mixes with drinking water lines. Every outlet, such as a hose bib, would need to be clearly labeled with signage like "Caution: Non-Potable Water - Do Not Drink." 

• DOH Guidelines: While not a formal regulation for onsite non-potable use, the Hawaii DOH provides guidelines for water quality parameters like turbidity and E. coli levels. Following these guidelines is highly recommended to ensure safety, especially in a school environment where children could accidentally come into contact with the water. 

• Code: UPC, IBC

Water Catchment System

• For irrigation (no treatment system)

• Water reuse & Stormwater control (requires extra capacity)

• Above grade

• Aeration system to keep water in good condition (it will smell without aeration)

• Training and manual for periodic filter cleaning

• Harvested Water (gal) = catchment area (sqft) x depth (in) x 0.623 (conversion factor)

  • Example: 20,000 sqft roof receiving 1 inch of rain equals 12,460 gallons of collected rainwater.

  • Geoportal Hawaii - Annual rainwater 

  • Central Maui = 20 inches/year

Greywater Recycling

• Wastewater from central Maui will be conveyed to the new central Maui Wastewater Treatment Plant (WWTP), where a portion will be reclaimed for non-potable uses. Therefore, the school’s plumbing infrastructure must be designed with a dual-piping system to accommodate water reuse. The potable and non-potable systems must be completely segregated from the initial construction phase. The design must facilitate a straightforward future connection of the non-potable piping network to the municipal recycled water supply once it becomes available.