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

[Update:  Be sure to check out the comments for this post, as there are additional tech details and resource links.]

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