USDA recommendation for water storage

[cmm1080]

I am trying to confirm the recommendation for drinking water storage as related to a distribution system. Is there a link anyone has that outlines this and other recommendations/guidelines?

I currently have that the USDA Rural Utility Service recommends 100 gal/capita/day for two days; however, I can't find that on their site and of course don't have any materials to back that up.

Thanks in advance.

 

[coloeng]

You should check with American Water Works Association (AWWA), which is an international organization that deals with all things drinking water,

http://www.awwa.org.

The capacity of storage necessary is usually specific to a particular system and should include both operating storage and emergency storage. Operating storage is used to provide water during the peak hours of the day, when demand exceeds the available supply. Without storage either your treatment plant or wells would have to constantly vary their production throughout the day to meet the changing demand. The tank then refills during the low demand periods. Emergency storage is used if your supply is interrupted or you need it for fighting a fire.

So you have to ask yourself, For my system, is 200 gallons per person a reasonable volume for both operating and emergencies? If you have 1 million people in your system, 200 million gallons may be excessive. If you only have 50 people, 10,000 gallons may not be sufficient.

 

[jgailla]

Also check NFPA 1, which has water supply requirements for fire protection.
If you just need a standard, try googling UFC-3-230-09A "Water Supply:Water Storage."
The UFC requires storage for 50% average daily domestic plus daily industrial plus fire protection.
coloeng makes an excellent point about the size of your system. These calculations are fairly straightforward for a small development of 1,000 or 10,000 people, but with a larger or smaller development you may have to adjust.
What size is your development? Is it residential, commercial, mixed use?

 

[cmm1080]

Thanks guys for the help...

The system has 1,324 current meters with 2.6 persons per household. Mixed use (2 commerical, 3 very large schools, and all others residential).

Nonetheless, I have a value of 688,480 gals needed at the present time per USDA recommendations for a 2 day storage. I've also got a design year value of 1,850 meters which will require a storage value of 962,000 gals.

I'm waiting for a call back on the schools' square footage to calculate the fire demand.

 

[semo]

You need to check with your USDA State Engineer if this is a USDA funded project or the State DNR/DEQ. They vary on what they want and who funds it.

In our state, we do not account for fire flow on any USDA design. Fire flow is extra that is only paid for with USDA loan money.

USDA looks at only the basic needs. The storage needed is based upon the maximum daily usage and available water supply pumping rate. These are used to determine the equalization storage needed for the tank(s).

Our state DNR looks at it differently and wants 1 average days usage as the minimum storage capacity.

 

[bimr]

I agree with what the previous posters have stated. You have to get the guidelines for storage from the agency that will approve your project.

Here is a link for the State of Washington's recommendations. The agency where your project is located should have something similar.

See chapter 5:

http://www.doh.wa.gov/ehp/dw/publications/design.htm