Inspection and Maintenance: Rainwater Harvesting

Inspection & Maintenance Guidance of Rainwater harvesting/cisterns best management practices. Rainwater harvesting is the practice of collecting, storing and making use of stormwater from roofs. Relatively clean roof runoff water is collected by eavestroughs or other types of roof drains, filtered to remove coarse debris, and conveyed to a structure where it is stored and drawn upon for purposes not requiring potable water (i.e. landscape irrigation, outdoor washing needs, fire suppression and toilet flushing (TRCA, 2018).

Overview

Rainwater harvesting/cisterns uses storage structures that can be installed either:

• Below-ground;
• Indoors that provide a year-round water source; or,
• Aboveground tanks and rain barrels that can only be used seasonally and must be taken out of service for the winter.

Rainwater cisterns can range in size from about 750 to 40,000 litres+ and may be constructed from fiberglass, plastic, metal or concrete. Underground cisterns are most often installed to a depth below the maximum frost penetration depth (generally 1.2 m in Southern Ontario) (Armstrong and Csathy, 1963; Ministry of Transportation, 2013) to ensure they can be used year-round. A pump is used to deliver the stored water to the hose bibs or fixtures where it is utilized. Water that is in excess of the storage capacity of the cistern overflows to an adjacent drainage system (e.g., other BMP or municipal storm sewer) via an overflow outlet structure and pipe. Cisterns that are drawn upon for indoor water uses (e.g., toilet flushing) will also feature water level sensors and the means of adding municipal water during extended periods of dry weather or winter when stormwater does not meet the demand (i.e., make-up water supply system). They may also include in-line devices to filter stored cistern water prior to delivery at hose bibs or fixtures.

• 

  Frost penetration in southern Ontario shown to be 2 - 4 ft. deep (Armstrong and Csathy, 1963).

• 

  Design depth showing further detailed frost penetration contour lines for southern Ontario ranging from 1.0 - 2.0m deep (Ministry of Transportation, 2013)

Generalized cross-section view of a rainwater harvesting system showing key components of a commercial configuration of this LID BMP (TRCA, 2018).

Some of the benefits of green roofs include:

• The ability to reduce the quantity of pollutants and runoff being discharged to municipal storm sewers and receiving waters (i.e., rivers, lakes and wetlands);
• Underground and indoor cisterns can be used year-round and located below parking lots, roads, plazas, parkland, landscaped areas or within buildings themselves.
• Can reduce a large commercial building or residential home's water usage significantly if used for non-potable needs
  

Key components of Underground Infiltration Systems to pay close attention to are the:

• Inlets
• Rain Barrel or Cistern|
• Pump
• In-line filters
• Overflow outlets

Associated Practices

• Rain Barrels Rain barrels are an above ground form of rainwater harvesting, typically used in residential settings. The precipitation flows from the roof, to the guttering and down the downspout before being diverted to the rain barrel for storage.
• Downspout disconnection Downspout disconnections are common in many older urban centers. They require that residents retroactively disconnect their downspouts from the municipal sewer system. This is due to older sewer systems being undersized for the combined flow of sanitary waste and stormwater.
• Blue roofs are systems that temporarily capture rainwater using the roof as storage and allow it to evaporate and/or to be used for non-potable requirements (i.e. irrigation, toilet flushing, truck washing) and ultimately offset potable water demands.

Inspection and Testing Framework

Visual indicator to be used when assessing the condition of a pretreatment device (in this case a downspout disconnection with attached filter) so that leaves and detritus from the eaves do not enter the Rainwater harvesting LID feature. Source: (STEP, 2018).

Visual Indicators Framework - Rainwater Harvesting Systems

Component	Indicators	Construction Inspection	Assumption Inspection	Routine Operation Inspection	Verification Inspection
Contributing Drainage Area
	CDA Condition	x	x	x	x
Inlet
	Inlet/Flow spreader structural integrity		x	x	x
	Inlet/Flow spreader obstruction	x	x	x	x
	Pretreatment sediment accumulation	x	x	x
Perimeter
	BMP dimensions	x	x		x
Overflow outlets
	Overflow outlet obstruction	x	x	x	x
	Control structure condition	x	x	x	x
Cistern
	Cistern structural integrity	x	x	x	x
	Cistern sediment accumulation	x	x	x	x

Testing Indicators Framework - Rainwater Harvesting Systems

Component	Indicators	Construction Inspection	Assumption Inspection	Routine Operation Inspection	Verification Inspection
Testing Indicators
	Sediment accumulation testing	x	x	x	x
Cistern pump testing		x	x	(x)
Note: (x) denotes indicators to be used for Performance Verification inspections only (i.e., not for Maintenance Verification inspections)

Construction Inspection Tasks

Example of a polyethylene cistern being installed during construction. During construction inspections it's important to note whether or not the depths, slopes and elevations are acceptable (Photo source: Innovative Water Solutions, 2021).

Construction inspections take place during several points in the construction sequence, specific to the type of LID BMP, but at a minimum should be done weekly and include the following:

1. During site preparation, prior to BMP excavation and grading to ensure that adequate ESCs and flow diversion devices are in place and confirm that construction materials meet design specifications
2. At completion of excavation and grading, prior to backfilling and installation of cistern and pipes to ensure depths, slopes and elevations are acceptable
3. At completion of installation of cistern and pipes, prior to completion of backfilling to ensure slopes and elevations are acceptable
4. Prior to hand-off points in the construction sequence when the contractor responsible for the work changes (i.e., hand-offs between the storm sewer servicing, paving, building and landscaping contractors)
5. After every large storm event (e.g., 15 mm rainfall depth or greater) to ensure Erosion Sediment Controls (ESCs) and pretreatment or flow diversion devices are functioning and adequately maintained. View the table below, which describes critical points during the construction sequence when inspections should be performed prior to proceeding further. You can also download and print the table here
   

Rainwater Harvesting Systems: Construction Inspections

Construction Sequence Step & Timing	Inspection Item	Observations*
Site Preparation - after site clearing and grading, prior to BMP excavation and grading	Natural heritage system and tree protection areas remain fenced off
	ESCs protecting BMP layout area are installed properly
	CDA is stabilized or runoff is diverted around BMP layout area
	BMP layout area has been cleared and is staked/delineated
	Benchmark elevation(s) are established nearby
	Construction materials have been confirmed to meet design specifications
BMP Excavation and Grading - prior to backfilling and installation of cistern and conveyance pipes	Excavation location, footprint, depth and slopes are acceptable
	Installations of underdrains/sub-drain pipes (location, elevation, slope) are acceptable
BMP Installation – after installation of pipes/sewers, prior to backfilling	Installation of structural components (i.e., pretreatment devices, inlets, cistern, overflow outlet, pump, make-up water supply and backflow preventer valve, control manhole/ access hatch) are acceptable and functioning

Routine Maintenance - Key Components and I&M Tasks

Regular inspections (twice annually, at a minimum) done as part of routine maintenance tasks over the operating phase of the BMP life cycle to determine if maintenance task frequencies are adequate and determine when rehabilitation or further investigations into BMP function are warranted.

Table below describes routine maintenance tasks for rainwater harvesting practices, organized by BMP component, along with recommended minimum frequencies. It also suggests higher frequencies for certain tasks that may be warranted for cisterns that receive flows from large roof drainage areas or roofs with mature trees near them. Tasks involving removal of debris, sediment and trash may need to be done more frequently in such contexts.

Rainwater Harvesting: Key Components, Descriptions and Routine I&M Requirements

Component	Description	Inspection & Maintenance Tasks	(Pass) Photo Example	(Fail) Photo Example
Contributing Drainage Area (CDA)	Roof area(s) from which runoff directed to the BMP originates.	Remove natural debris and sediment annually to biannually; Trim back tree boughs that hang over the roof area to reduce maintenance needs.	CDA has not changed in size or land cover. Sediment, trash or debris is not accumulating and point sources of contaminants are not visible.	Size of the CDA has changed from design assumptions. A point source for contaminants is visible (i.e. lack of sediment controls on adjacent construction site). (Photo Source: North Carolina Cooperative Extension)
Pretreatment	Devices prevent debris and sediment from entering the BMP. Includes eavestrough or downspout screens, first flush diverters or filters on pipes leading to or from the cistern. Reduce the risk of obstructing inlets, intakes or overflow outlet pipes and excessive sediment accumulation.	Remove trash, debris and sediment biannually to quarterly or when the device sump is half full; Measure sediment depth or volume during each cleaning, or annually to estimate accumulation rate and optimize frequency of maintenance.	Forebay is free of sediment, trash and debris and recently maintained. The large stones in the feature are used to slow down and spread out inflowing water into the feature and they remain well arranged and in place.	An erosion gully occurring where bare soil is starting to become visible on the grass filter strip pretreatment feature at the inlet, thus indicating it is not effectively slowing and spreading out the inflow of stormwater to the BMP.
Inlets	Pipes connected to eavestroughs or roof drains that deliver water to the BMP. May also include a pipe connected to the municipal water supply line for maintaining cistern water level during dry weather.	Check for obstructions and remove any debris or sediment annually to biannually; For outdoor above-ground cisterns and rain barrels, inlets need to be disconnected in the late fall/early winter, prior to the onset of freezing air temperatures; Reconnect outdoor above-ground cisterns to the roof drainage area in the spring once air temperature remains above freezing.	There is no evidence of damage or displacement of the inlet structure that would prevent runoff from freely entering the BMP.	Accumulated sediment and vegetation is preventing stormwater from entering the BMP. Sediment on the pavement surface in front of the inlet indicates ponding is also occurring
Access Hatch	Hatch, manhole or lid that provides access to the interior of the water storage structure.	Inspect for damage, obstruction and accessibility annually.	The footprint area of the bioretention cell does not significantly deviate from the final design and should not negatively affect its stormwater management treatment performance.	The footprint area of the BMP is significantly smaller than what was specified in the final design of this example and differ greater than the recommended SWM criteria requirements (>10%).
Cistern or rain barrel	The water storage structure (e.g., concrete vault, fiberglass, plastic or metal tank, rain barrel).	Inspect for damage or leaking annually; Drain and remove accumulated sediment as needed (annually at a minimum).	There are no erosion gullies or bare soil areas on the filter bed surface and mulch cover remains in place.	Erosion gullies and bare soil areas are present on the filter bed surface, indicating that concentrated flow occurs regularly into the BMP feature. (Photo Source: CVC).
Pump	Pressurized device used to deliver stored rainwater to the hose bibs.	Inspect and test for proper function annually.	The planted portion of the bioretention cell is completely covered with dense, attractive vegetation which helps to maintain its stormwater treatment function and aesthetic value.	A larger portion of the bioretention cell has no vegetation cover which reduces its aesthetic value and could be negatively affecting its stormwater treatment function. Much less than 80% of the planting area is covered by living vegetation requiring immediate maintenance and reseeding.
Filter	Cisterns may include an in-line filter device on the intake pipe or prior to delivery of rainwater to hose bibs.	Remove debris and sediment biannually to quarterly or as directed by the system manufacturer.	The overflow outlet is free of damage and obstruction and functions as originally designed.	The overflow outlet is partially obstructed with trash and debris which reduces its capacity to safely convey excess water from the BMP, likely due to excess ponding thus obstructing outflow and impairing overall drainage function of the BMP.
Overflow Outlet	Pipe connected to the cistern or rain barrel that conveys overflows to another drainage system (e.g., municipal storm sewer or other BMP).	Check for obstructions and remove any debris or sediment annually to biannually.	The well is undamaged and accessible and the cap is in place and secured to prevent unauthorized access.	The well standpipe has been damaged by snow plowing, which impairs its use for monitoring and is a safety hazard. With the cap unable to be secured unauthorized access can also occur.

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.

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.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

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

Toronto and Region Conservation Authority

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

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

A system flow of gully inlets, pipes, overland flow paths, open channels, culverts and detention basins used to convey runoff to its receiving waters. City of Toronto 45 Wet Weather Flow Management November 2006

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

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

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.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Watercourses and Lake Ontario, to which Stormwater and Combined Sewer Overflows discharge.

Any form of rain or snow.

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

Sustainable Technologies Evaluation Program

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.

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.

Structure to control the volume or rate of flow of water through or over it.

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.

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 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.

The total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Stormwater Management

a top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales.

Credit Valley Conservation

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.