Gravity fed water supply

   / Gravity fed water supply #1  

ewhyte

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Jul 4, 2007
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12
Hello All
I would like to start a discussion about gravity fed water supplies. First question to put out there...
What height should the water source be above the point of consumption?

In my case, I have an excellent spring that is 77' feet above my ground level at my home. The spring is about 2300 feet from the house. I propose to use a 2" diameter pipe as there will likely be at least 3 families using the supply at some point in the future.

Is 77 feet high enough? Do you think I should add a pump at the house to keep pressure consistent? What psi will 77 feet provide?

Friction losses will be minimal given the larger pipe diameter.

Cheers and thanks,
Eric Whyte
 
   / Gravity fed water supply #2  
77 feet should be high enough, but you need capacity to build pressure.
'100 gallons of water@77 feet will supply some pressure, while 5,000 gallons@77 feet while provide lot's of pressure'

I do not know exact figures(or even close), but anyone figuring it will need the amount of water you are holding at the top.

EDIT: I do know that if the holding tank is large enough, no pump will be needed at the house.
 
   / Gravity fed water supply #3  
.4 psi or so per foot with pressure losses for friction, turns, valves.
 
   / Gravity fed water supply #4  
My grandparents farm was gravity fed. Rough calculations would be 50-60 feet above faucet and about a 1000' run. They built a concrete square "well" around the spring. I remember the water pressure being impressive. They had a bathroom on both floors plus kitchen and summer wash area. The run forked and a pipe was sent to barn approx 90 ft from the house.

I wish I had this set up. No worries about power outages. Great spring fed water and lots of it. Good luck with this.
 
   / Gravity fed water supply #5  
You are looking at 33 psi at 77'.
As long as you do not have high rates of flow, that psi should not see much drop. High rates of flow, then you will have friction losses. If you will need more flow, then possibly even bigger diameter pipe would help you out.
 
   / Gravity fed water supply #6  
77 feet should be high enough, but you need capacity to build pressure.
'100 gallons of water@77 feet will supply some pressure, while 5,000 gallons@77 feet while provide lot's of pressure'

I do not know exact figures(or even close), but anyone figuring it will need the amount of water you are holding at the top.

EDIT: I do know that if the holding tank is large enough, no pump will be needed at the house.

Water pressure is 0.433 psi per foot of head, so 77 ft * 0.433 psi / ft = 33.3 psi. It does not matter if the tank holds 100 gallons or 1 million gallons of water, if the head is the same the pressure will be the same.

This is the static pressure, at high flow rates there will be frictional losses.
 
   / Gravity fed water supply #7  
My inlaws lived in the house my mother inlaw was born in until they passed away. They never had a water pump. It was all gravity fed from a spring in the field above the the house. They did not have a lot of pressure but a with all post depression folks just lived with it. When we put a modular home on a full basement next door I dug a hole and planted a 1200 gal plastic water tank and put a submersible pump in a piece of 8" pvc pipe with a pitless adapter and ran it into a bladder tank in the basement. We have great pressure and great water. I ran an inch line from the tank 200 feet to a creek for an overflow from the tank, but got to thinking it was a shame to waste all that water that was just running down the creek when the tank is full so I went to Tractor Supply and bougfht a stock tank float valve so it shuts off the flow when the tank is full. When I need to clean out the reservoir up at the spring I just unhook the float valve and let it run to the creek. The reservoir up at the spring is a brick and concrete affair that is a four foot square that is about eight feet deep. In the past when it silted in I helped my father inlaw empty it out with a rope and a bucket the spring flows hard enough that it was always about a 3 hour job getting it drained enough to clean it out. I plan to drain it down by just letting it go out the overflow in my tank at the house. If that don't work fast enough I will take my generator a hose and a small sump pump up to the spring. I haven't had to clean it out for several years, but when the neighbor gets the beans off this fall I will have to do it as it is starting to silt up. Rural life is great just takes a little more work than living in town.
 
   / Gravity fed water supply #8  
just something to think about

When you run your main line consider burrying a secondary line even if it is only 3/4" and use it to monitor overflow, it won't rob anything from your source but it will give you a heads up if there is a problem at the source.
I run an "overflow" tube into a "birdbath" on my property whenever the overflow line quits for more than a while (based on the flow from the spring) I know I should investigate.
 
   / Gravity fed water supply #9  
My water supply is a spring 75' above my house. I ran a 3 inch line down 900 feet because I get my power from it as well as water. With 2x 3/4 inch jets running full time making electricity I still have more pressure at the taps in the house than any city water source I have ever had.
Rick
 
   / Gravity fed water supply #10  
My parents has gravity fed spring and it was like that when theey bought the house. It is not on a steep hill like yours and you are lucky. they have it over 1000 ft in zig zag pattern thru a 1/2" pipe on a run that is probably 8 ft slope underground and then finally empties into a holding tank. a cheap shallow jet pump is used to pump water into the house. Since its been over 50 years like this, the pipe has rusted to a point where it trickles during the summer time but they still have alternate source of water if needed. I am amazed its still delivering water , but I know there is impending doom soon, question is when?

As for your situation, if the familys don't depend on your water source for water pressure and let it go to a holding tank in home, you probably will be ok for 3 people and up. Of course you will need to set a hose for overflow and let it run out to a local pond or something. it will be interesting on how you plan to divert water evenly for 3 homes.
 
 
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