How Do I Budget for a Commercial Rainwater Harvesting System?
February 7, 2019
The Real Costs of Rainwater Collection and Reuse for Commercial Properties
Rainwater harvesting systems are becoming more common due to stormwater management requirements, limited storm sewer capacity, climate change, and sometimes the desire for a more sustainable approach to managing our water resources.
Rainwater harvesting should be a vital part of any commercial building’s water management program. Rainwater harvesting can make a significant impact in several key areas including:
- stormwater management compliance,
- flood reduction/protection,
- reducing demand and stress on municipal/regional infrastructure,
- reducing municipal potable water costs,
- meeting sustainability goals, and
- generating a positive return on investment.
Accurate Budgeting for a Commercial Rainwater Harvesting System is Crucial
Accurately budgeting for rainwater harvesting systems is imperative. It’s important to understand the important design elements required for budgeting for a rainwater harvesting system. It is crucial to budget properly to reduce costly change orders and minimize the potential for construction delays.
Budgeting for a commercial rainwater harvesting system goes beyond pricing out a cistern, pump, and filtration system. Each rainwater harvesting system is site-specific and the omission of certain key elements can lead to under-estimating budgets and/or poorly functioning or non-operational systems.
6 Steps to Budgeting for a Commercial Rainwater Harvesting System
Step 1: Determine Cistern Size and Location
The budget price of the cistern will depend on the material selected. For buried cisterns, typical fabrication choices are concrete and fibreglass. Concrete cisterns may generally cost less but the location of a site, soil characteristics, and groundwater elevation may increase cost or eliminate concrete as a feasible choice. For above ground installation, fibreglass, high density polyethylene, and steel tanks can be considered. Above ground tanks can significantly reduce your installation budget but the compromise will be space.
Step 2: Determine the End Use
Knowing the end use is an important piece to determine the magnitude of disinfection required. For example, the disinfection for drip irrigation would be different from vehicle wash due to the higher likelihood of contact with the rainwater in aerosol form. In general, the higher the potential to end use exposure by consumption, inhalation or dermal contact, the higher the level of disinfection required to protect human health. The purpose of disinfection is to inactivate or remove viruses, bacteria and opportunistic protozoa to a level fit for use. If the end use is drip irrigation, then no disinfection is required since the potential for exposure is unlikely. In contrast, water sprayed for vehicle wash has a higher likelihood of being inhaled and come in contact with skin therefore proper pre-treatment and disinfection is required and would add cost to the budget.
Step 3: Determine the Water Quality in Cistern
Understanding potential contaminants that can get captured in the cistern is another very important consideration. When it comes to selecting treatment systems, one size does not fit all. Once the end use and raw water quality is determined or estimated, then the type treatment process can be designed to fit the end use. Source water quality is one of the most important consideration when budgeting a rainwater harvesting system as it affects the magnitude of treatment required.
Step 4: Determine the Peak Flowrate for the Application
The peak flowrate required for all the fixtures is an important design detail which will heavily influence the configuration and size of a rainwater harvesting system. The peak flow can be calculated by adding up the number of fixtures and multiplying them by their respective water supply fixture units (WSFU) which can be found in your local plumbing code. Knowing your peak flowrate will help a designer strategize on treatment configuration to minimize cost.
Step 5: Determine the Total Dynamic Head (TDH) to the Farthest Fixture
Based on the non-potable water (NPW) distribution network in the mechanical plans, determine the total dynamic head (TDH) from the rainwater harvesting system to the farthest fixture located at the highest elevation. Generally, if the TDH at the discharge of a rainwater harvesting treatment system is more than 165 feet, it will likely add cost to the budget.
Step 6: Determine the Level of Automation/Controls Required
The level of automation is an important consideration from an operations and maintenance point of view. The more critical the water supply, the more automation is suggested as it provides more operational and monitoring flexibility. Automation can reduce operations and maintenance costs by keeping the user informed of system performance and only alerting and alarming when operator attention to the system is required.
Getting Your Rainwater Harvesting System Budget Right
Every site has different, specific requirements for a rainwater harvesting system to function optimally. So, it is important to understand what impacts overall cost. To find out more detail about the 6 steps, download the Guide to Budgeting Your Commercial Rainwater Harvesting System. This in-depth guide to budgeting for your commercial rainwater harvesting system provides:
- an introduction to rainwater harvesting and the important role it plays in water resource management,
- an overview of the components of a commercial rainwater harvesting system,
- steps to budgeting for a rainwater harvesting system including a budgeting worksheet, and
- an outline for implementing a commercial rainwater harvesting system.