Alternative Water Source Systems
5 Things a Project Developer Should Keep in Mind
5 Things a Project Developer Should Keep in Mind
By Vijay Sundaram and Wendy Chen
The drought in the western United States grabbed everyone who relies on water by the shoulders and screamed ‘WAKE UP!’ It was an intervention. No more taking the supply of water for granted in the great western desert. The more your project depends on a water source you don’t control, the more vulnerable it is. And let’s face it, if your project is a heavy water consumer in an increasingly conservation-conscious world, your project will be outstanding but for all the wrong reasons.
Simple rainwater capture systems have been around for centuries. But in arid regions, rainwater alone may not get you where you want to go. Improvements in treatment technology make water reusepossible and perhaps practical: Use the same water multiple times and you multiply your local supply; multiply your local supply and you reduce your reliance on water. Additionally, you’re a very good neighbor when your many stakeholders, be they employees, residents, or the local community, all applaud you for your commitment to water stewardship efficiency.
There are basically five categories of alternative water source systems: 1) rainwater harvesting, 2) gray water systems, 3) black water systems, 4) foundation drainage systems, and 5) stormwater capture and reuse systems. Gray water doesn’t include wastes from toilets, dishwashers, kitchen sinks and utility sinks; black water does.
Given the emerging business case for building water supply efficiency/resiliency into new construction, it’s important to understand the options, not just in terms of initial capital cost but lifecycle cost and risk. Here’s a basic primer to get you started:
1. See Past the Buzzwords
“Net-zero sounds good. Let’s do that.” Net-zero or ‘water neutral’ means no water is needed by the project after construction, except for rainfall on the building site and an emergency water connection for fire suppression.
With net-zero, it’s all about the volume of rainfall, the catchment area for gathering rainfall on your project site, using that water efficiently, and effectively removing contaminants and pathogens from the same water allowing its continual use and reuse. An example from a California-based project in a semi-arid setting is presented in Figure 1.
Under the current water conservation requirements, the project would have a net withdrawal from groundwater resource of 105 Mgal/year. Three tiers of alternative water source projects were developed to allow the project to reduce its net withdrawals to 50, 28, and 0 Mgal/yr in a phased manner as appropriate.
2. Create a Checklist
When considering alternative water source systems for your project (up to possibly net-zero water), there are fundamental principles involved that serve as a business case analysis checklist:
- Simply ask the question: Are alternative water source systems the right choice for your project? Systems can be selected based on project size or local requirements, but what is your situation? Should each development have its own facilities (with relatively poor economy of scale), or should developments (or the entire city/community) join together to provide the same services from a centralized system? Centralized facilities may offer better overall economies of scale. The answer is very situation specific.
- List and understand all of the appropriate local, state, and federal regulations so you can assess the true lifecycle cost, including ongoing O&M, and compliance risks.
- Water conservation and reuse can be phased over time to respond to regulatory changes, stakeholder preferences, and finances, as shown in the example in Fig. 1.
- Create a project-specific water budget — including climatic conditions. Similar to a financial budgeting process, the water budgeting process reveals the project viability and the performance forecast, and quantifies overall benefits.
- Perform a cost-benefit analysis involving capital costs and ongoing annual operation, maintenance, monitoring and compliance costs, and overall benefits from implementing alternative water source systems. Then put that cost into the context of your project and the soft factors that position it in the marketplace.
3. Develop a Project Water Budget
The starting point for implementing an alternative water source project lies in creating a detailed water budget specific to the project and its associated property uses (e.g., roads, parking areas, sidewalks, landscaping). That budgeting process should include:
- Potable water and other waters brought to the property (e.g., groundwater, reclaimed wastewater, raw water).
- Rainfall, rainfall runoff coefficients for all building and property surfaces, and evaporative losses of rainfall from those wetted surfaces.
- Wastewater and stormwater releases/exports from the building and property.
- Evapotranspiration from indoor and outdoor landscaping.
- All water uses in the building and property: cooling water, wash, irrigation, food prep, sinks, toilets, showers, etc. With this identification of uses, note should be made of the quantity and quality of water needed for the use.
With the initial water budget completed and shown as both a numeric tabulation and figure (a simplified example of a water budget figure is shown in Figure 2), the building developer, architect, and water engineer can begin to develop meaningful water conservation and reuse measures and associated costs, regulatory requirements, and staffing requirements.
4. Keep It Simple and Safe
After preparing a water budget, it’s easy to focus on matching the available alternative water sources to specific end uses based on water qualities (e.g., dual pipe systems based on gray water, adding two piping system inside the building). However, too many water supply and wastewater collection systems in a project or campus increase the risk of cross-connections, maintenance issues and liability. Keep it simple and safe.
5. Keep a Tidy House
Though project-specific alternative water source systems are relatively small-scale compared to centralized citywide water reuse systems, both are designed and implemented based on the same principles with similar components (e.g., treatment units and conveyance systems). Consequently, alternative source systems should be planned and designed with worker safety, ease of operation, and reliable compliance in mind.
Ongoing monitoring and documentation requirements can be significant depending on local regulatory requirements. Main regulatory concerns related to alternative water source systems include: cross-connection (i.e., risk of alternative water source mistakenly being connected to potable water system), pathogens (germs such as Legionella), fouling in pipes and treatment processes, and system reliability. Alternative water source systems can be designed to address the regulatory concerns; however, ongoing preventative maintenance and upkeep is key to maintaining compliance. Slime growth within alternative water source systems is a common problem, which can be addressed by implementing a comprehensive preventative maintenance and monitoring program.
Building in water supply resiliency/water efficiency is increasingly good business. But water is so critical to life and health and is so closely regulated that both the lifecycle cost and the risks need to be properly understood and planned for. The opportunities are now greater than ever.
About the Authors: Vijay Sundaram is a water reuse technology leader, and Wendy Chen an environmental services senior associate, both with Stantec, a global engineering, consulting, and design services company.