Low Impact Development Manual for Michigan - OSEH - University ...

Design Considerations
Design and installation procedures for capture reuse
containers can vary from simple residential rain barrels
to highly engineered underground systems in ultraurban
areas. Table 7.5 provides general information
on cistern holding capacity. The following procedures
should be considered when designing sites with capture
reuse containers.
1. Identify opportunities where water can be reused
for irrigation or indoor greywater reuse and then
calculate the water need for the intended uses. For
example, if a 2,000 square foot landscaped area
requires irrigation for four months in the summer
at a rate of one inch per week, the designer
must determine how much water will be needed
to achieve this goal (1,250 gallons per week,
approximately 22,000 gallons for the season), and
how often the storage unit will be refilled with
precipitation. The usage requirements and the
expected rainfall volume and frequency must be
determined.
Table 7.5
Round cistern capacity (Gallons)
Height
(feet)
6-foot
Diameter
12-foot
Diameter
Source: The Texas Manual on Rainwater Harvesting
18-foot
Diameter
6 1,269 5,076 11,421
8 1,692 6,768 15,227
10 2,115 8,460 19,034
12 2,538 10,152 22,841
14 2,961 11,844 26,648
16 3,384 13,535 30,455
18 3,807 15,227 34,262
20 4,230 16,919 38,069
2. Rain barrels and cisterns should be positioned to
receive rooftop runoff.
3. If cisterns are used to supplement greywater needs,
a parallel conveyance system must be installed
to separate greywater from other potable water
piping systems. Do not connect to domestic or
commercial potable water system.
4. Consider household water demands (Table 7.6)
when sizing a system to supplementing residential
greywater use.
Table 7.6.
Household water demand chart
Fixture Use Flow Rate
LID Manual for Michigan – Chapter 7 Page 152
Toilet
Shower
Bath
Faucets
Washing
Machine
# flushes per person
per day
# minutes per
person per day
(5 minutes
suggested max.)
# baths per person
per day
Bathroom and
kitchen sinks
# loads per day
1.6 gallons per flush
(new toilet)
2.75 gallons per
minute (restricted
flow head)
50 gallons per bath
(average)
10 gallons per day
50 gallons per load
(average)
Dishwasher # loads per day 9.5 gallons per load
Source: Philadelphia Stormwater Manual
5. Discharge points and storage units should be
clearly marked “Caution: Untreated Rainwater, Do
Not Drink.”
6. Screens should be used to filter debris from runoff
flowing into the storage units. Screens should be
made of a durable, non-corrodible material and be
easily maintainable.
7. Protect storage elements from direct sunlight
by positioning and landscaping. Limit light into
devices to minimize algae growth.
8. The proximity to building foundations should be
considered for overflow conditions. The minimum
setback distance for capture and reuse systems is
10 feet.
9. If the capture and reuse system or any elements of
the system are exposed to freezing temperatures,
then it should be emptied during the winter months
to prevent ice damage.
10. Cisterns should be watertight (joints sealed with
nontoxic waterproof material) with a smooth
interior surface.
11. Covers and lids should have a tight fit to keep out
surface water, insects (mosquitoes), animals, dust,
and light.