While the capital cost of wastewater treatment is a significant deciding factor, seek technologies or strategies that have low maintenance requirements to keep operations and maintenance costs low. Alarm systems for malfunctioning wastewater treatment systems can be expensive, be sure to research this. 

Treating wastewater simply for sewage conveyance can be expensive, so make the most of tertiary-treated wastewater by using it for as many non-potable water applications as possible—irrigation, toilet flushing, and cooling tower makeup water.

Determine how treated wastewater will be used onsite. It must either be reused, such as for toilet flushing or irrigation, or must be infiltrated onsite. 

Verify that your onsite wastewater treatment system is capable of treating the wastewater to tertiary standards. State governments determine exactly what constitutes “tertiary treatment” based on allowable remaining levels of certain nutrients and organisms. Your civil engineer will need to be in charge of this determination. 

Determine what type of onsite wastewater treatment is most appropriate for your project. Typical septic-tank-and-leachfield systems used in many rural areas where there are no sewer systems do not treat water to tertiary standards so they can’t be used to earn this credit. 

Even if you are attempting Option 2, you will want to select water-efficient fixtures, which minimize the quantity of wastewater treated onsite. To accomplish this, target the most consumptive fixtures to achieve the greatest water reduction, but keep in mind the very different maintenance requirements for waterless fixtures. See WEp1 and WEc3: Water Use Reduction for more information. Also, review the Option 1 steps of this credit.

Option 2: Treat 50% of Wastewater Onsite to Tertiary Standards

Compare the baseline and design case water budgets to determine the water reduction percentage for your project. The LEED Online credit form has a built-in calculator to facilitate this calculation. Repeat this process until selection of water fixtures and strategies is finalized and your project’s water reduction goals have been met. 

Typically, dual-flush and composting toilets have a higher cost over conventional fixtures but reduce water charges. Some ultra-low-flow toilets have a cost premium as well, but it is typically not as significant as a dual-flush or composting toilet. 

A dual plumbing system and rainwater or graywater reuse are likely to add upfront costs but the owner may recoup some of that cost in reduced water and sewer charges. However, most current utility rates for water and sewer are too low to justify these systems on a cost basis alone.