Rainwater Harvesting for Michigan Homes

What would it cost to build a water-catchment system for a home in SE Michigan? Code and other such issues will vary widely, but the actual construction costs are likely to be relatively uniform. I recently discovered that the city of Guelph, Ontario has done some great forward thinking work on encouraging rainwater catchment for their residents. I emailed the folks at Guelph, and they referred me to Ben Polley, a builder with Evolve Builders. Ben provided me with these excellent details about their cost and performance estimates.

Note that these figures include a good number of caveats about current unknowns and several costs that are not included, but they give us a good start on tracking down the overall costs. If you have additional data to round this picture out more, please let us know in the comments below.

Also, see my personal post about how this could be used in Detroit (including costs and references for going completely off the water grid) over at the SkyTalk blog at lagomorph.org.

Ben writes:

Hi Jacob,

In a former life, I used to perform work on the refrigeration systems in ice rinks in both Ann Arbor and Novi, MI. From that experience, I would expect that the pricing in formation below will be reasonably consistent with what you may find in Michigan too.

I have included below for your interest some excerpts of a design study we performed for a southern-Ontario project and the resulting price proposals. You will note that there are multiple items not considered in the quote that would yet further impact on final cost of construction though are difficult to assess unless aware of the full context of the work (eg. is it being performed at the same time as other excavating work in the example of a new home or is it a retrofit; whether one uses indoor storage tanks or an exterior buried cistern; which is more important, ensuring maximum utility of captured water or ensuring minimum number of “dry days” where water must be made up by other sources, etc).

So while these excerpts may also result in as many questions as it may answer, it should at least provide you with a ballpark starting figure for a couple of different types of system for a few different options of roof captured surface areas.

And then he provides those clips from the study:

Project Calculations:

OPTION 1: Active Storage Tank volume = 3200L
Performance parameter	Unit	House + Garage	House only	Half House + Garage	Half House only	Garage only
Catchment area	m2	254	200	154	100	54
% of user demand met	%	98%	98%	97%	91%	68%
% of rain utilized	%	28%	35%	45%	67%	95%
Number of dry days	-	7	9	14	37	137
Number of overflow events	-	74	64	51	28	3
Volume of rainwater used	m3	52	51	51	48	36
Volume of overflow	m3	135	96	63	25	2

OPTION 2: Active Storage Tank volume = 6400L
Performance parameter	Unit	House + Garage	House only	Half House + Garage	Half House only	Garage only
Catchment area	m2	254	200	154	100	54
% of user demand met	%	100%	100%	99%	97%	70%
% of rain utilized	%	29%	36%	47%	71%	99%
Number of dry days	-	1	1	2	13	126
Number of overflow events	-	74	63	49	24	1
Volume of rainwater used	M3	53	52	52	51	37
Volume of overflow	M3	134	95	61	22	0

% of user demand met – the percentage of all toilet flushes supplied solely by harvested and stored rainwater annually

% of rain utilized – the amount of water harvested with available tank storage capacity relative to overall amount of harvested water

Number of dry days – the number of days in a year where the cistern may not have sufficient water to handle the assumed usage

Number of overflow events – the number of rainfalls that fill storage tanks to capacity with additional water being sent to overflow

Volume of rainwater used – the annual volume of water harvested and stored in the tanks then used by the proposed fixtures

Volume of overflow – the annual volume of water harvested but sent to overflow after filling storage tanks to capacity

	EVOLVE RAINWATER HARVESTING SYSTEM

ITEM	INDOOR SYSTEM DESCRIPTION	OUTDOOR BURIED SYSTEM DESCRIPTION

Snow Capture	extra by others	extra by others
Winter Optimization	extra by others	extra by others

Coarse Prefiltration	Leaf Flusher at 6 downspouts, all on either	Leaf Flusher at 6 downspouts, all on either
	the south side or north side only	the south side or north side only
Transport of Water	yes, including above-grade penetrations	yes, including foundation penetrations
Cistern	2 x 1300 litres	1 x 6300 litres c/w 24″ riser
	space required 6′-6″x7′-0″, 32″ door access	tank size 102″x72″x78″H, bury 24″ deep
	access path required along one short side	installed within 15′ of building
		minimum 24″ separation from septic lines
Overflow Protection	yes with floor drain by others	yes, via leaching pit or gravity drain
Fine Filtration	Yes	none
Calming Inlet	Yes	yes
Drought Protection	automatic	automatic
Water Treatment: micron filter	none required	none required
Water Treatment: carbon filter	none required	none required
Disinfection: UV disinfector	none required	none required
Plumbing to Fixtures	fixture feeds from RWH pump by others	fixture feeds from RWH pump by others
	pump requires 3′-0″x3′-0″ adjacent to cistern	pump requires 3′-0″x3′-0″ adjacent to
		foundation penetrations

Electrical	extra by others	extra by others
Plumbing	fixture feeds & auto make-up extra by others	fixture feeds & auto make-up extra by others
	Mains shutoff must be functional for retrofits	Mains shutoff must be functional for retrofits
Site Management	n/a	site visit to ensure satisfactory excavation
Excavation & Fill	n/a	trenching, excavation & tank base fill extra
		by others. Groundwater drainage if req’d
		extra by others.

Price for above:	$8,980 +GST	$10,750 +GST

OPTIONAL	INDOOR SYSTEM	OUTDOOR SYSTEM
Indoor Tank Shade Cover	If open to sunlight, add $200 per tank	N/A
Aditional Tanks	Each 1300 litre tank, add $1350	N/A
Larger Tank	N/A	Increase tank to 12,600 litres, add $2400
Level Gauge	N/A	Add $300