Stormwater Management Systems

Wahaso Stormwater Harvesting Systems

While “rainwater” and “stormwater” are terms that are often used interchangeably, there is a difference between the two. “Rainwater” is the relatively clean water coming from rooftops and “stormwater” is more contaminated water coming from landscapes, sidewalks, parking lots and other grade-level surfaces.
Stormwater Harvesting Systems

Stormwater Harvesting

Depending on the site, stormwater detention or stormwater collection areas can be quite large and often contain contaminants such as silt, hydrocarbons and fertilizers in their stormwater harvesting system. Increasingly, communities are requiring developers to manage their stormwater runoff in order to reduce the load on the local storm system with a stormwater management system.

Wahaso’s stormwater system not only accommodates large quantities of stormwater but provides more robust treatment designed to handle difficult contaminants. The result is a system that provides a safe, treated supply of water that can be used for a variety of non-potable applications.

More and more communities are requiring developers to manage the run-off from their impermeable rooftops, hardscapes and parking areas to reduce the impact of the run-off on municipal treatment systems. This requires builders to install storage tanks that slowly release collected stormwater into surrounding waterways to protect the municipal treatment facilities from high stormwater flows.

This storage can require an investment of hundreds of thousands – or millions of dollars to filter the stormwater, remove hydrocarbons and then detain the treated water until the storm event has ended. Normally these detention systems represent a “sunk cost” from which the property owner will receive no direct benefit.

Turning a Liability into an Asset

Wahaso sees this detention stormwater as an asset rather than just a liability, and offers solutions that filter, sanitize and pressurize the water for on-site reuse. Harvested stormwater can be used for any number of purposes. Irrigation is the most common use, but this valuable resource can also be used to flush toilets, make-up water in evaporative cooling towers and more. Not only does this harvesting effort save the building owner thousands of dollars a year in water bills, but the practice reduces the burden on the municipal treatment system and saves the energy needed to transport and purify that water at the remote plant. It’s a sustainable practice that benefits property owners and the greater community.

Economics and Return on Investment

For large stormwater detention systems, the incremental cost for converting the storage from detention to retention for harvesting is a small fraction of the cistern cost. For example, a 400,000-gallon detention cistern might cost $500K or more. Adding a harvesting capability to irrigate the property’s landscaping could be $50K or less – a 10% increase in total system cost — that would yield savings year after year in municipal water and sewer charges. And because the detention systems are usually mandated by local codes, they are a sunk cost when calculating the ROI of the incremental harvesting capability. Wahaso can provide a detailed ROI analysis for any project through our Scoping process to estimate total water savings.

Stormwater Detention System Design

Stormwater collected from large properties, parking lots or watersheds can be contaminated with sediment, hydrocarbons, debris and other pollutants. In order to reduce maintenance on the cistern, it is important to pre-filter the stormwater.

Wahaso recommends the Nutrient Separating Baffle Box (NSBB), which utilizes screening and hydrodynamic separation to capture the pollutants common in stormwater. The NSBB stores debris in a dry state, minimizing bacterial growth and nutrient leaching in the water.

The proprietary treatment train of Wahaso’s stormwater system is IAMPO 324 certified and filters the harvested water down to 0.02 microns, removing suspended solids as well as bacteria and viruses. Filtered water is sanitized using Ultraviolet (UV) and if required, chlorine, and is then sent to the end use or stored in a processed water holding tank to await re-pressurization.

The treated water is safe and suitable for non-potable applications such as toilet flushing, irrigation and cooling tower make-up.


IAPMO 324 Certified

A system with third party certification can provide peace of mind that a system is reliable and safe. The Wahaso stormwater system has IAPMO 324 certification, meeting or exceeding all of the standard’s requirements.

System Benefits

  • Turn a Liability into an Asset. Stormwater management often requires a detention system to hold the water for a period of time and release it slowly to the municipal storm system. Instead of releasing the water, why not retain it for reuse? The Wahaso stormwater harvesting system provides a way to collect and treat that water, providing a more sustainable and cost effective solution to stormwater management.
  • Scalable. The Wahaso stormwater system can be Scaled to treat from 2,000 to 200,000 gallons per day or more.
  • Low Maintenance. The system has been designed to run reliably for long intervals, with minimal maintenance required.
  • Robust Controls. Wahaso’s proprietary control system is custom programmed to monitor and track all system activity.
  • Integrated System Design. Wahaso’s stormwater processing skids are pre-assembled and integrated into comprehensive system designs that include all pumps, storage, filtration, sanitation and controls.

Standard Systems

Wahaso’s stormwater system is fully scalable and able to process 2,000 – 200,000 gallons per day. Each standardized system includes the filtration and sanitation equipment. The customizable equipment includes tanks, pressurization and controls.

For more information on our stormwater harvesting systems, download the information sheets.

Optirtc Technology

Municipalities that require stormwater detention raise a fundamental issue of turning stormwater detention into retention for reuse:
Detention Capacity
If stormwater is retained in the cistern for reuse, there may not be sufficient detention capacity to meet the detention requirement for the next storm event, defeating the purpose of the detention capacity. That could mean that the developer would have to add redundant storage capacity for the retention portion, negating the benefit of leveraging the required detention for reuse. Many communities won’t count cisterns used for retention to qualify for required detention.
The OptiRTC system
To resolve this issue, Wahaso has teamed up with OptiRTC as a key component in our stormwater harvesting solutions. The OptiRTC system uses predictive weather models and complex algorithms to anticipate storm flows to detention in order to determine how much capacity is required to meet the detention requirement before the storm begins. The smart system then measures the retained stormwater and, if necessary, opens a remote valve to release a set amount of stored water before the rain event begins. That ensures that the expensive storage capacity can serve as both detention and retention space.

Pre-treating Stormwater

It is key for any storage system that the water entering the cistern be properly pre-treated.
Pre-treating Stormwater
This means that a filtration process needs to remove hydrocarbons, debris, sediment and pollutants before the water enters the tank. If the water is coming off rooftops and other non-parking areas, this may be as simple as passing the water through a screen or vortex filter. Contaminants from parking areas need special treatment to remove the additional contaminants that may be present.

For parking stormwater and high-capacity flows from large rooftops, Wahaso likes the Nutrient Separating Baffle Box system developed by Suntree Technologies. These systems utilize screening and hydrodynamic separation to capture pollutants in stormwater.

Patented Screening System
The patented screening system, suspended above the sedimentation chambers, captures and stores trash and debris in a dry state. Dry state storage of trash and debris minimizes nutrient leaching, bacteria growth, bad odors and allows for easier removal. Trash, debris & organics are captured in the filtration screen as sediments settle to the bottom chambers. This separation prevents odor, bacteria growth and nutrient leaching in the water. The NSBB systems are constructed with pre-cast concrete and available in sizes to handle 1-15 CFS and more, removing hydrocarbons and TSS (Total Suspended Solids) to 125 microns.

Storage Options

There are many systems suitable for storing treated stormwater for reuse. Our most common methods include underground fiberglass tanks, concrete vaults and the Atlantis D-Raintank system.

We like the Atlantis D-Raintank system because of its design flexibility, low cost compared to other options and its interactivity as a storage system. Stormwater stored in the Atlantis D-Raintank system can be retained for reuse by adding an impermeable liner to the excavation. Water quality is maintained in the cool and dark cistern and improved through capillary action and microbe interaction in the surrounding compacted material. Sand is compacted around the sides and top of the storage tank between the permeable geotextile liner around the tank and the impermeable containment liner. Surface water can enter the tank directly by filtering through the compacted material above the tank, and water in the tank is able to interact with the compacted material on the sides. This action helps keep the water in the tank oxygenated and microbes in the soil layer act on organic material in the cistern to further purify the stored water. For information on additional storage methods, visit our Storage Options page.

Stormwater Processing

Treated stormwater typically has two uses: for sustainable irrigation, and to source an on-site rainwater harvesting system. Both applications require different processing methods.

Sustainable Irrigation
After detained stormwater has been filtered, we then sanitize the water using ultra violet light—a chemical free, low maintenance approach to sanitation. This process kills any harmful bacteria or pathogens in order to meet health codes and ensure that the water is safe for spray irrigation systems. Submersible pumps are stainless steel with variable frequency drives and are used for pressurization. The sub-surface placement of the system reduces system footprint and allows complete flexibility in the location of the processing skid.

Rainwater Harvesting Systems
Pre-treated stormwater can also be used to source a rainwater harvesting system for application in toilet flushing, cooling tower make-up and more. Water is sanitized using UV light as described above, or chlorination, a common approach that uses sodium hypochlorite to produce a highly concentrated chlorine liquid. This chemical is similar to that used in a municipal water treatment systems but is in a form that is safer and easier for building maintenance staff to handle. Water must then be pressurized at a flow rate that is determined by its intended application.

Wahaso Stormwater Management Systems FAQ’s

Wahaso is happy to talk with you about how we might help you convert your stormwater detention to retention and reuse through harvesting. Please contact us.

1. What is stormwater harvesting used for?

Stormwater harvesting involves collecting rainwater at grade to meet various water demands, including irrigation, washing, drinking, and cooling. This includes pervious and impervious areas like walkways, lawns, decks, parking lots grade. The four key components of stormwater harvesting are:

  • Storage/cistern – This may be above ground, below ground, concrete vault, modular, corrugated, HDPE or fiberglass
  • Filtration – This includes pre-filtration prior to water going in the cistern and the type of filtration depends on the type of water and where the system is located
  • Sanitation – This can be either UV light, chlorine, ozone or cupridyne
  • Controls – Measures tank levels, flow rates, water savings and pump and system statuses.
2. What is the difference between rainwater harvesting and stormwater management?
Stormwater management involves collecting, treating, and reusing stormwater runoff from various ground surfaces such as lawns, gardens, footpaths, driveways, and roads. While rainwater is similar to stormwater management, it involves water collected from rooftops instead of drains and ground surfaces. A key difference is in the level of contamination of the water. Rainwater tends to be far cleaner and simpler to process than stormwater.
3. Why is stormwater harvesting important?
Stormwater harvesting has a wide range of benefits. Besides offsetting municipal water uses and its costs, it helps reduce the volume of contaminated stormwater discharged into the environment. Stormwater harvesting plays a critical role in reducing the risk of flooding and maintaining the hydrological cycle. In addition, reducing the stormwater load on a building site can provide tax credits and save on retention and detention costs.
4. How do stormwater harvesting and reuse work?

Stormwater harvesting and reuse is an intricate system involving the collection, treatment, storage, and use of stormwater runoff. The four main stages of this system are:

  • Collecting the stormwater from a source, such as a drain
  • Temporarily holding the water in a below- or above-ground storage
  • Treating the water to reduce pathogens and contaminants
  • Distributing the treated water for non-potable reuse
5. Can stormwater be used for irrigation?
Irrigation is one of the beneficial uses of stormwater. It is the most cost-effective option for commercial property owners looking for an affordable water source for landscape irrigation. Stormwater can also be used for toilet flushing, cooling tower make-up and a variety of other non-potable uses.
6. How does stormwater management help control flooding?
Areas that uphold proper stormwater management have a low risk of flooding and are less likely to suffer the detrimental effects of flooding. Urban and developed areas with less vegetation and more impervious surfaces prevent rainwater from naturally soaking into the ground. The water runs rapidly into sewer systems, drainage ditches, and storm drains, increasing the risk of flooding and run-off into adjacent waterways.
7. Are surface water and stormwater the same?
There is a difference between stormwater and surface water. Surface waters refer to ponds, streams, and lakes. Stormwater comes from rain and snowmelt and eventually drains into surface waters. Therefore, it is critical to ensure clean stormwater to minimize surface water pollution.
8. What is the only liquid that should enter the stormwater system?
Clean rainwater is the only liquid that should be the output of a stormwater harvesting system. Therefore, it is important to filter out pollutants such as oils, bacteria and other contaminants.
9. How can stormwater be reused?

There are numerous ways to reuse stormwater. These include indoor and outdoor applications.

Indoor uses

  • Toilet Flushing
  • Washing machines
  • Cooling Tower Make-Up
  • Fire suppression
  • Process and boiler water

Outdoor uses

  • Irrigation
  • Fire fighting
  • Sanitary sewer flushing
  • Street cleaning and dust control
  • Vehicle and building washing
  • Water features
10. What contaminants can be found in stormwater?
Stormwater can contain a wide range of contaminants, including chemicals, bacteria from pet waste, fertilizer residue, paint, oil, and grease. Other common pollutants include sewage overflow, styrofoam cups, cigarette butts, fast food wrappers, and construction debris.
Tags: Best Rated Stormwater Management, Stormwater Harvesting Systems

Since 2004

Wahaso Mission

Our mission at Wahaso is to help municipalities and commercial property owners reduce the impact of their buildings on the environment through innovative and sustainable water practices.