Ask a Techspert: How does a building become “water positive”?

Our new Bay View campus is on track to be the largest development project in the world to achieve Water Petal certification from the Living Building Challenge, meaning it will meet the definition of being “net water positive.” That important sustainability effort moves us closer to our 2030 company goal of replenishing more water than we consume. But what exactly does “water positive” mean at Bay View? District Systems Water Lead Drew Wenzel dove into that question head first.

Let’s get right to it: What does “water positive” mean?

“Water positive” at Bay View means we will produce more non-potable water than we have demand for at the Bay View site.

Hmm, let’s back up: What’s non-potable water again?

There are a couple of types of water. There is potable water, which is suitable for human contact and consumption, and there is non-potable water, which is not drinking quality but can be used for other water demands like flushing toilets or irrigation.

Typically, buildings use potable water for everything. At Bay View, we have an opportunity to match the right quality of water with the right demand, and only use potable water when it’s necessary. And by over-producing non-potable water, we can share such excess with surrounding areas that might otherwise rely on potable water for non-potable needs.

So basically, are we helping the water system save high-quality water?

Right. In California, we’re years into our most recent drought. We’re only going to see increasing pressure on water resources. Regional and State water agencies are working hard to secure the potable water supply. We believe we can best support these public-sector efforts and increase potable water supply by using non-potable water where we can.

So how did we get to water positive for Bay View?

This may be surprising, but it actually all starts with the geothermal energy system. Typically, removing heat from a building is done through evaporating a lot of water via cooling towers. At Bay View, instead of doing that, the geothermal system removes almost all heat by transferring it into the soil beneath the building. This system eliminates at least 90% of the water needed for cooling, or about 5 million gallons of water per year.

Ok, we start by reducing water use. What’s next?

After improving the water efficiency as much as we could through the geothermal system and other measures, we looked at the water resources we have on site. By collecting all of our stormwater and wastewater and treating it for reuse, we are able to meet all of our onsite non-potable demands.

How do we treat it?

Stormwater treatment starts with the retention ponds that collect rain. Water from these ponds is slowly drawn down and pumped to a central treatment plant, where it goes through several stages of filtration, treatment and disinfection.

All of the wastewater — from our cafes, restrooms and showers — is collected and sent to the central plant, where it undergoes two stages of filtration and treatment. From there, the water goes out to a field of reeds that naturally pull out nutrients, creating a perennial green landscape that supports local wildlife. Finally, the water is sent back to the plant again for final treatment and disinfection.

The final output from both stormwater and wastewater treatment processes is recycled water that meets State regulations for non-potable use.

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