Catchment Water System Design

Eric's Catchment Water System Thoughts

Topographic Map with House Each Line is Five Feet Water meter and electricity currently on lot, catchment water tanks and possible wind turbine for agricultural use. North-most 20,000 gallon tank uses 5,580 sq. ft. roof water from house and optional storm drain runoff. A second 6,000 gallon tank near workshop is fed from 1,250 sq. ft. workshop and lath house roof.

Agricultural water sources:
1. House Roof catchment
2. Barn Roof catchment
3. Road runoff (filtered, used only for emergencies)
4. Kahakuloa Acres Private Water (via float valve in water tank)

Kahakuloa Acres Private Water Company (KAPWC) provides a maximum of
311,000 gallons potable treated well water per year ($6.00 / 1000 gallons)

Catchment sources for agricultural use (House):
Horizontal roof projection: 5500 sq. ft.
One inch rainfall / sq. ft = 5/8 gallon
e.g. 40 inches rain / year on 5500 sq. ft. = 137,500 gallons / year
Assume 80% efficiency (losses due to evaporation, absorption, gutter spill, etc,) = 110,000 gallons / year (agricultural use only)

Catchment sources for agricultural use (Barn):
Horizontal roof projection: 1250 sq. ft.
Assume 90% efficiency (metal roof) = 28,125 gallons / year (agricultural use only)

Second source:
Easement for road storm drain (agricultural use only, minimal use of street - only four houses on street above lot.)
Aprox. 14,000 sq. ft. road between storm drain and next highest storm drain
40 inches rain / year on 14,000 sq. ft. = 350,000 gallons / year
Assume 70% efficiency (losses due to evaporation, absorption, etc,) = 245,000 gallons / year (agricultural use only)

Average Rainfall (inches):		House Roof (gal)	Barn Roof (gal)	Street (gal)
January	6.2	17,050	4,359	37,975
February	4.4	12,100	3,094	26,950
March	4.8	13,200	3,375	29,400
April	4.4	12,100	3,094	26,950
May	2.1	5,775	1,477	12,863
June	0.9	2,475	633	5,513
July	1.5	4,125	1,055	9,188
August	1.7	4,675	1,195	10,413
September	1.4	3,850	984	8,575
October	3.0	8,250	2,109	18,375
November	4.4	12,100	3,094	26,950
December	5.2	14,300	3,656	31,850
Yearly Total	40.0	110,000	28,125	245,000

Catchment water stored in 20,000 and 6,000 gallon tanks.
Top of tank 14 ft. below house and 10 ft. below storm drain outlet.
Gravity fed irrigation with automatic timers and rain sensors to areas below tanks.
Pumped with solar-powered 12V Shurflo Aquajet ARV Variable Speed
RV demand pumps (5.3 GPM, 10 Amp., 80 PSI [184 ft. head])
with automatic timers and rain sensors to areas above tanks.