Rainwater Harvesting: Performance

TSS Reduction

The performance results for Rainwater harvesting practices, located within TRCA's watershed originate from fours sites:

• Minto Hotel (Toronto)
• Metro Label 1 (Scarborough)
• Metro Label 2 (Scarborough)
• Brookside P.S (Scarborough)

The mean performance value recorded at each of the rainwater cistern practices, was to measure their ability to remove Total Suspended Sediments (TSS), which was calculated based on 24 separate recordings from 2007-2010 at each of the aforementioned locations listed above.

As can be seen in the corresponding boxplot the mean performance removal efficiency of the rainwater cistern practices monitored are well below the suggested guideline of 30 mg/L (Canadian Water Quality Guideline (CWQG), or (background (assumed at <5 mg/L)+ 25 mg/L for short term (<24 hour) exposure) (CCME, 2002; (TRCA, 2021).

The median value of the 24 samples taken was 1.25 mg/L whereas the mean was 3.98 mg/L, with a 4% guideline exceedance.

Phosphorus Reduction

The performance results for Rainwater harvesting practices, located within TRCA's watershed originate from fours sites:

• Minto Hotel (Toronto)
• Metro Label 1 (Scarborough)
• Metro Label 2 (Scarborough)
• Brookside P.S (Scarborough)

The mean performance value recorded at each of the rainwater cistern practices, was to measure their ability to remove Total Phosphorus (TP), which was calculated based on 24 separate recordings from 2007-2010 at each of the aforementioned locations listed above.

As can be seen in the corresponding boxplot, the mean performance removal efficiency of the infiltration trench practice monitored is not meeting the acceptable upper extent range of nutrients as it is 0.03 mg/L (30 µg/L) (Environment Canada, 2004; OMOEE, 1994).

The median value of the 24 samples taken was 0.05 mg/L whereas the mean was 0.11 mg/L, with a 100% guideline exceedance. Given the small sample size of just 24 grab samples further monitoring projects will be required to ensure that the results collected are as accurate as possible to ensure these practices can meet federal and provincial governments' guideline requirements for TP stormwater quality.

Please refer to the Phosphorus page and the additives page for more information on how LIDs can reduce contaminant loading in stormwater

Recent Performance Research

• (O'Hogain et al. 2012) - Physicochemical and microbiological quality of harvested rainwater from an agricultural installation in Ireland
  • This research study conducted by the Dublin Institute of Technology was commissioned by the federal government to assess the feasibility of utilizing rainwater to replace treated mains for non-potable uses (bathing, irrigation, etc.) on an agricultural property. Two different rainwater harvesting configurations were developed and the results collected over a 1-year period found that median TSS levels were 3.0 mg/L for configuration 1 and 3.5 mg/L for configuration 2. The only parameter that did not comply with local drinking water regulations were the levels of iron, lead and ammonia collected in the cistern of configuration 1 and just ammonia for configuration 2 (O'Hogain et al. 2012).

Schematic drawing of a RWH system with larger capacity for residential or commercial usage. In this schematic pre-storage filtration is used to prevent excess sedimentation, leaves and detritus from entering the system. A piping network delivers water to the tank and a first flush diverter can be installed to diver the first 1-3 mm away from the storage container and be deposited as overland flow, preserving the quality of water for later use (DeBusk and Hunt, 2014.

• (Knights et al. 2012) - Can rainwater tanks meet multiple sustainability objectives?
  • This paper presents results of a study that highlight the benefits of rainwater tanks and harvesting systems in urban environments. The results come from real-time metering and usage of rainwater by a household that is a part of a rainwater tank program in Marrickville, Australia. 10 samples were taken from the tank and found that a mean level of 5 mg/L of TSS was found, while 0.054 mg/L was found for TP. The removal total for hte tank on an annual basis was found to be 240,000 mg/yr (TSS) and 2,000 mg/yr of TP (Knights et al. 2012.

• (Kus, et al. 2011) - Water Quality in Rainwater Tanks in Rural and Metropolitan Areas of New South Wales, Australia
  • This study compared RWH in Sydney and Kangaroo Valley, Australia and their ability to remove common pollutants found in rainwater collected from rooftops. TSS rates ranged predominately between 0.5 - 3.5 mg/L in most Sydney-area RWH tanks, but increased to +5.5 mg/L in others that were above local turbidity levels set by the Australian Guidelines for Water Recycling (AGWR). Meanwhile all samples taken from New South Wales based RWH never exceeded 1.0 mg/L. Additionally the authors conducted experiments on collected rainwater from a typical domestic roof in Sydney, New South Wales and treated it with an adsorption pretreatment filter media system of granular activated carbon (GAC), followed by micro-filtration. The influent rainwater was quite low already (1.2 mg/L), but the GAC pretreatment achieved an average reduction to 0.79 mg/L (~34% removal efficiency) removal efficiency and with the membrane filtration it reduced TSS to less than 0.5 mg/L (below instrument detection limits). therefore removal efficiency couldn't be accurately applied but greater than 58% (Kus, et al. 2011).

Total suspended solids

Toronto and Region Conservation Authority

Tank used to store rainwater (typically roof runoff) for later use.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Total phosphorus

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

Rainwater harvesting.

The technique of removing pollutants from runoff as it infiltrates through the soil.

Deposition of material of varying size, both mineral and organic away from its site of origin by the action of water, wind, gravity or ice.

Settling-out or deposition of particulate matter suspended in runoff.

The delivery of a disproportionately large load of pollutants during the early part of storms due to the rapid runoff of accumulated pollutants. The first flush of runoff has been defined several ways (e.g., 10 mm per impervious area).

Initial pulse of stormwater runoff which picks up the pollutants that have settled on surfaces during the dry period. The first flush contains the highest pollutant concentrations.

Open space floodway channels, road reserves, pavement expanses and other flow paths that convey flows typically in excess of the capacity of the Minor Drainage System.

The attachment of gas, vapour or dissolved matter onto the surface of solid materials.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

A biological community, including humans and their natural environment.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

Reduction in applied water due to more efficient water use such as implementation of Urban Best Management Practices or Agricultural Efficient Water Management Practices. The extent to which these actions actually create a savings in water supply depends on how they affect net water use and depletion.