5.4 Non-Potable and Reclaimed Water Strategies

The Strategy Layer Above Fixtures and Cycles

Fixture swaps and cycles of concentration get a project to the prerequisite floor and the early credit points. To reach 2 points outdoor, 5-6 points indoor, and the second cooling tower point, projects typically replace some potable demand with non-potable water sources.

The Five Non-Potable Sources

1. Rainwater Harvesting

Roof runoff is collected, screened, and stored in cisterns or tanks. Typical system components:

• First-flush diverter — sheds the first volume of rainfall (usually 0.05-0.1 in) carrying roof contaminants away from the cistern.
• Leaf screen and filter before the inlet.
• Storage cistern sized by water budget calculations (use vs. supply curves across the year).
• Pump and pressure tank for distribution.
• Backup potable connection with backflow preventer for dry periods.
• For indoor use: filtration plus disinfection (UV, chlorine, or ozone) to meet local non-potable water quality standards.

Typical end uses: irrigation, toilet flushing, cooling tower makeup, vehicle wash water.

2. Graywater

Graywater is lightly used wastewater from:

• Bathtubs, showers, lavatories
• Clothes washers

It does not include: kitchen sinks, dishwashers, or toilet/urinal effluent (those are blackwater). Graywater systems require:

• Diversion plumbing — separate drain lines from blackwater.
• Surge tank to hold incoming graywater.
• Filtration (typically sand or membrane) to remove hair, lint, soap residue.
• Disinfection for indoor reuse.
• Purple-pipe distribution and signage to prevent cross-connection.

Typical end uses: toilet flushing, subsurface drip irrigation.

3. Blackwater Reuse and On-Site Treatment

Blackwater treatment systems take all building wastewater (graywater + toilet/kitchen) and treat it to a reuse standard. Approaches include:

Living Building Challenge projects often pair these with composting toilets to fully close the water loop.

4. Condensate Recovery

When warm humid air contacts cold cooling coils in HVAC equipment, water condenses out — sometimes thousands of gallons per day in large or humid-climate buildings. Condensate is essentially distilled water (low dissolved solids) and is ideal for cooling tower makeup because it raises achievable cycles of concentration.

Key design points:

• Slope condensate pans and lines to a collection sump.
• Plumb to cooling tower basin or non-potable holding tank.
• Add overflow to the storm drain for excess.

5. Municipal Reclaimed Water

Where utilities offer it, purple-pipe reclaimed water is treated wastewater delivered to building sites for non-potable uses. Because the utility has already treated it to a state-regulated reuse standard, the project's only requirements are:

• Backflow prevention at the building connection.
• Purple-pipe identification and signage.
• No cross-connection with potable plumbing.

Reclaimed water counts toward the 100% outdoor reduction (Option 2, 2 points) and toward the 20% non-potable makeup for the cooling tower 2-point option.

Comparing Sources

Code, Health, and Verification Considerations

• State plumbing codes vary widely. Some states (e.g., Texas, Arizona, California) have explicit graywater statutes; others restrict graywater to subsurface irrigation only; some prohibit indoor reuse entirely.
• International Plumbing Code (IPC) Chapter 13 and Uniform Plumbing Code (UPC) Chapter 16 address non-potable water systems — required treatment, signage, dyeing, and backflow prevention.
• EPA WaterSense labels apply not just to fixtures but also to irrigation controllers and irrigation professionals — specify WaterSense-certified components to claim higher irrigation efficiencies.
• All non-potable systems require backflow preventers at the potable interface and clear labeling (purple pipe, signage) at every accessible component.
• Verification at LEED documentation requires system schematics, water-budget calculations, permits, and treatment-system specifications — auditors look for evidence the system actually delivers the claimed gallons.

Pulling It All Together

A high-performing LEED BD+C project usually layers strategies:

Low-flow WaterSense fixtures + dual-flush + waterless urinals
  -> meet 35-45% indoor reduction
Graywater or rainwater for toilet flushing
  -> push to 50% indoor reduction (6 pts)
Rainwater/condensate for cooling tower makeup at >20%
  -> earn 2nd cooling tower point
Reclaimed water or 100% non-potable irrigation
  -> earn 2 outdoor points
Sub-meters on irrigation, hot water, cooling tower, fixtures
  -> earn metering point

That full stack adds up to roughly 9-11 of the 11 WE points while staying inside common code constraints.