Presented by: Brian SoderholmWater Control Corporation

1500 year-old, 21 million gallon Basilica Cistern in Istanbul, Turkey.

• How big of a rainwater cistern to use?• What to do with rainwater?• What are other sources of reclaimable water?• Where can I use graywater?• What are the benefits and payback?• What about sanitation?  Is it safe?• How to collect the water?• How to store the water?• How to best disinfect the water?• How to best deliver the water to fixtures?• What system options are available in the market?• What about code compliance?

You May Have Major Questions!

• 1 ft²

roof surface can generate approximately 0.62 gallons of 

usable water per inch of rainfall.•Example: a 15,000 ft²

roof in MN could generate approximately 

15,000 X 4.34 X 0.62 = 40,362 gallons in an average July.

• A 40,000 gallon cistern may not be practical in a wetter climate.• Only full after spring snow melt or major

storm!• Fixtures/equipment may not require so much water• (in a dry climate, size near 100% and look for other sources)

• Wetter Climate Rule of Thumb:  divide total gallons by avg. 

peak monthly rainfall events – ex. For MN: 2 or 3 (i.e. 20,000 or 

13,ooo gallon cistern) and compare to gal. required.

• Choose the smaller of the two when sizing cistern.

• Cooling System Condensate:• 0.1 gal/ton hour at 70% relative humidity• 0.2 gal/ton hour at 80% relative humidity• 0.3 gal/ton hour at 90% relative humidity

• Challenge: low pH, bacteria

• Cooling Tower Blowdown• Challenge: high TDS, chemicals

• Groundwater • Challenge: soil‐based minerals

• Softener/Filter Backwash• Challenge: suspended solids and high TDS (depending 

on type of filter)

Other Potential Sources:

• Rainwater can be collected and re‐used for:• Landscape irrigation• Cooling tower/Boiler make‐up water• Tanker filling/ Backup fire systems• Nursery irrigation systems• Flushing toilets and urinals• Vehicle washes• Industrial process

• Potable water applications not recommended – and 

probably not legal!

Many Potential Uses:

Graywater Reclamation:

• Graywater = Water from showers, bathroom lavs, clothes washers, (possibly pool backwash).

• Reclaimed for sub-surface irrigation and (possibly) fixture flushing

• Toilet/urinal flushing requires disinfection and is only legal/possible without special approval in IPC (and IPC-based) states!

Graywater System Design Considerations:

• Enough storage for 1 or 2 days’ demand (code dependent).

• Tank water should turn at least every 3 - 7 days (code dependent).

• Overflow to sanitary sewer

• No blackwater! (toilet, kitchen sink, laundry with diaper service, etc.)

• Occupant # / Graywater discharge estimation tables in UPC and IBC

• Up to 12+ LEED™

points may be available:• “Stormwater

Design: Quantity/Quality Control (2)”• “Water Efficient Landscaping (4)”• “Innovative Wastewater Technologies (2)”• “Water Use Reduction (4+)”• A virtual MUST

for LEED™

Gold and Platinum 

certification!

• Potential for drastically reduced sewer/water impact fees

• Reduced water and sewer fees• Calculating “payback”

requires number crunching!• Good systems: $2000 ‐

$200,000

• Public health risks:

• Bacteria, algae, pathogens, mold, insects, rodents, 

(and almost anything else imaginable) seem to find 

their way into cistern/storage tanks (ask your 

grandparents!).

• Graywater

is of particular concern.

• Cooling towers and irrigation systems can 

diffuse these harmful agents into the air (think 

Leigionella

bacteria!).

• Toilets, urinals, and other fixtures supplied with 

reclaimed water can cause internal contact with 

these agents.

= Potential for major liability!

Sanitation

Designing a System: The 4 Concerns:

• Collection

• Storage

• Treatment

• Delivery

Thoughts on Collection:

• Consider roof drains with mesh screens if debris on roof will be minimal

• Pre-filtration is always highly recommended!

• Water from drain tiles may contain iron or other minerals (extra filtration required)

• Water from parking lots not recommended:• May contain salt, oil, antifreeze, trash, goose feces, etc.

Thoughts on Storage:

• Polyethylene, fiberglass, corrugated (lined), galvanized steel or concrete tanks (verify compatibility with disinfection method)

• Buried or located indoors in northern climates

• Overflow, vent, manhole access, and inlet/outlet tappings required

• If above-ground, consider black or green color to prevent algae growth

• Chlorination (oxidation):

• Advantages:• Measurable• Residual disinfection 

• Disadvantages:• Not terribly “green”

(LEED®)

• Chemical handling and storage• Not good for landscaping• Expensive/ongoing chemical purchase• Trihalomethanes

(THM’s) and other 

harmful byproducts!• Only ClO2 effective with algae

•Calcium hypochlorite tablets•Sodium hypochlorite solution•Chlorine gas•Chlorine dioxide solution

• Ultraviolet (DNA destruction to prevent replication):

• Advantages:• No chemicals• Relatively low cost and                              

maintenance up to 80 GPM systems

• Disadvantages:• No residual disinfection (circulation highly 

recommended!!!)• Ineffective if water is discolored or turbid (UV 

sensor highly recommended!!!)• Not as effective with viruses or cysts

• Ozonation

(oxidation using O3):• Advantages:

• No chemicals –

generated on demand• 2000 times faster than chlorine• Back to O2 in approx. 17 minutes• Residual disinfection• Powerful deodorizer• Works in dirty/discolored water• Measurable • May help with Green Roof discoloration

• Disadvantages:• More $$ and maintenance if under 80 GPM• Cistern cannot be vented indoors w/o destructor

Thoughts on Delivery:

• pH may be an issue! (consider appropriate piping materials!). Ozone/ chlorine also corrosive.

• Particulate filtration needed prior to delivery (cartridge, bag, basket, or membrane filter)

• Most states have strict marking requirements (“Non-Potable Water”)

• Incorporate a fresh-water bypass or make-up if tank goes dry, disinfection goes down, etc.

• Ensure appropriate backflow prevention! (RPZ assembly or “break tank” with air gap).

So How Are People Doing It?

• Individual component systems designed in-house (contractor builds)

• Residential or light commercial “rainwater harvesting kits”

• Large commercial turnkey systems

• Code Issues:

• A lack of clarity and consistency in state codes can lead to 

confusion, delays,  and disapprovals.

• Public health concerns• Confusion at state, engineer, customer and inspector 

level

• Current code status:• IPC: Rules for graywater

only – no rainwater• UPC: Rules for graywater

and municipally treated 

wastewater.  Rainwater code currently under development• Draft codes being developed by ARCSA, IAPMO• California Title 22 statutes and USEPA 2004 Guidelines 

for Water Reuse

•Plan Review is the norm!  The more robust a system, the less likely 

you are to experience hang‐ups at state or inspector level!!!

What About The Codes???

Questions?