Designing low-impact, integrated water systems can contribute to net-zero water and energy goals, and create buildings and sites that are sustainable, resilient, and that connect people to natural water processes.
Water is a critical natural resource that touches and influences the design of all buildings and sites, and designers can positively influence the management of water resources. Water, energy and carbon are acknowledged to be fundamentally linked, often referred to as the water-energy nexus. Smart water management in design can serve both to reduce energy demands associated with water transport, treatment and use, and to sequester carbon within the open spaces that we preserve, restore and construct.
Why are water systems critical to managing climate change?
As designers, we tend to think about water within two key systems: building systems and natural systems. Both systems influence the carbon cycle in different ways.
Water in building systems is the water that flows in pipes to serve uses such as drinking water, plumbing fixtures, mechanical equipment, and irrigation systems. We think about these water uses as “transactional” because the water is taken out of a natural system at a carbon cost (the energy required for pumping and water treatment) and returned at a typically higher carbon cost (the energy required for pumping and wastewater treatment prior to discharge back into a natural water body). Conservation and reuse of water can reduce the long-term operational carbon footprint of a project, along with a myriad of other benefits.
Water moving within natural systems supports life (flora and fauna), which in turn bolsters the natural sequestration of carbon by vegetation, which captures carbon dioxide from the atmosphere and transforms it into biomass through photosynthesis. Natural water systems are those supported primarily by precipitation and stormwater runoff. These systems differ from transactional water systems in that they are less “engineered,” typically influenced only in the ways we shape a site and manage the stormwater runoff. Well-designed stormwater management strategies should mimic natural hydrologic processes to the degree feasible by slowing, spreading, infiltration and evapo-transpiring water. Critical to these processes are healthy soils, which carry the lifeblood of our natural systems. Disrupting proper hydration of soils through increased impervious cover, compaction, and depletion alters the connectivity of natural systems both above ground (i.e. rate and volume of runoff to surface waters) and below ground (i.e. infiltration and recharge to groundwater). The integration of low-impact site design, stormwater management, and landscape architecture are critical success factors for how our projects will perform in this regard.
While we often think about these water systems separately, they are intrinsically interlinked and water systems should be planned and designed in an integrated way that allows for maximizing benefits to both the built and natural environment, while minimizing energy use, disruption of natural processes, and contribution to climate change.
"The hydrologic cycle shows us that all water is already recycled water. It re-circulates throughout our planet, changing form and location. But the amount of water on Earth has not and will not change. Every drop of the water we drink, every drop we flush down our toilets, every drop we use to shower, wash our clothes, irrigate our lawns, and grow our food—all water on the planet—has been used and treated and recycled, countless times."
... water and wastewater treatment systems speed up this cycle, and many treatment systems mimic natural processes in increasingly innovative ways.
Reference: https://worthenfoundation.org/water-reuse-practice-guide
How has climate change impacted the way we manage water?
Over the past decades, climate change has altered the hydrological cycle leading to more intense rainfall events (increased runoff and flooding risks) as well as longer periods of intense droughts (increased water scarcity). This “feast or famine” cycle is only expected to intensify with climate change into the future. Heightened attention to water scarcity and extreme weather events has sparked changes in the way we design buildings, and the way we manage water. Incorporating innovative water management strategies that are holistic, and go above and beyond minimum code compliance, may incur upfront capital costs, but these costs can often be offset by long-term operational savings as well as a decrease in upfront gray infrastructure costs (e.g. pipes, underground infrastructure). Key elements that influence building and site design include:
Aggressive water conservation: Designers can greatly impact a project’s water footprint through the implementation of water conservation with minimal impact to cost. Low-flow, high performing plumbing fixtures and high-efficiency mechanical equipment can go a long way to reduce a project’s water footprint without significant cost increases. Likewise, irrigation demands can be optimized through the use of native planting palates and efficient irrigation systems (drip systems, soil moisture sensors, etc.), as well as stormwater management strategies as discussed below.
Onsite non-potable water systems: These systems collect wastewater, stormwater, or rainwater and treat it so that it can be reused in a building, or at the local scale for non-potable needs such as irrigation, toilet flushing, and cooling. Technologies and codes have evolved to allow for water treatment and reuse to be implemented at “site” or “district” as compared to municipal scale water infrastructure systems. Onsite water reuse can improve project sustainability by introducing closed-loop systems and reducing the need for long-distance conveyance and pumping to and from municipal water and wastewater treatment plants (and the associated energy/carbon impact).
These systems have both upfront capital costs and long-term operational costs that need to be considered when designing a project. Low tech, passive systems are typically considered for smaller systems while larger building and district projects often implement engineered treatment technologies such as membrane bioreactors (MBRs). Building-scale reuse can become cost effective when a project exceeds approximately 35,000 gallons per day of non-potable water demand (on the order of a 300-unit residential building with some irrigation and cooling). Operational savings are realized through reduced potable water and sewer discharge fees to the local municipality; with the quickly escalating cost of these services, onsite systems are becoming increasingly financially viable.
Stormwater management and resilience: Climate drivers are impacting the way we think about stormwater conveyance, management, and natural systems. Climate change is predicted to increase peak storm intensities and frequency of large storm events, which can cause detrimental flooding and damage to both buildings and natural systems. Sustainable site planning and integration of landscape architecture with stormwater management is becoming increasingly critical to mitigate these climate impacts and improve project resilience. Natural systems not only mitigate flooding risk, but also contribute to reducing climate impacts and enhancing habitat, as noted above.
Coupled with sustainable site design, stormwater practices that focus on the creation of resilient natural systems require negligible, if any, additional cost for implementation and operations. By taking cues from permaculture practices, project costs can even be reduced by encouraging sheet flow onto adjacent landscapes to spread and soak water into the landscape, thereby reducing reliance on underground piping and engineering stormwater treatment approaches.
Where to start
Spend time to understand the local context of your projects as related to their transactional and natural water systems.
Start with a design focused on conservation and efficiency.
Create a project water budget considering all supplies (precipitation, wastewater, greywater, etc.) and demands (potable, non-potable, interior, and exterior). A water budget will help designers determine the best use of the project’s water resources, and whether alternative strategies such as rainwater harvesting or onsite reuse may be beneficial to the project. Many factors influence sustainability and feasibility of onsite systems, a few of which include:
Approach site design with natural system function at the heart of the design. Make sure your civil engineer and landscape architect are working together in lockstep.
Highlight the overlapping project benefits:
Tools and resources
Stormwater and natural systems:
An Introduction to Permaculture
Sustainable Nation, Wiley & Sons, Douglas Farr, 2017
Onsite reuse:
https://worthenfoundation.org/water-reuse-practice-guide
https://www.sfpuc.org/sites/default/files/documents/OnsiteWaterReuseGuide2022.pdf
