How to gauge over-land elevation gain for gravity fed water system pressure? : LUSENET : Countryside : One Thread

How can we gauge the elevation gain fairly accurately on our land? We must install a gravity feed water system (no power to property) and I think I've read somewhere that you need 2 feet of elevation for every 1 foot of water pressure desired. The portion of our property where we will be putting the house/water system is gradually sloping but how can we tell how much elevation is gained over a certain area?

-- Lisa (, February 08, 2002


Lisa: One pound of water pressure is roughly equal to 27" of height or "head". I'd suggest going to the nearest rental place and see if they have a surveyors transit for a real accurate measurement. Using that you should be able to discern how much "drop" you're gonna have over the distance the water has to travel.

There's another way that'll be cheaper(almost no cost) but it'll take some dinking around. Get a line level (about $1) and some strong cord. Secure one end of the cord to the ground where you wanna start the measurement. Then run it out as far as practical, level it with the line level, making sure its really tight, then measure the distance from the ground at that point to the line. You might wanna take a 6'-8' pole with you to tie the measured end off to, once level. It'll make measuring easier and more accurate.

Write down the results and start the process over again with the anchored end of the line now at the last measured point. Repeat this process till you've gotten to where you need to be and total the measurements to give you the fall or head in inches and divide by 27" to get PSI.

This won't be a dead-on measurement but you'll be in the ballpark if you're careful with the line level, keeping a tight line when you're measuring.

-- john (, February 09, 2002.

Lisa, water weighs 62.4 lbs/sq. ft. Since a sq. ft. is 144 sq. in. That gives you .43 lbs/sq. in. or psi at the bottom of a one foot high container filled with water to the top.

If you need 40 lbs of pressure in your house the vertical elevation would be 40/.43 or 93 ft. If you can find or rent a Locke level which is a small hand held level you sight through, you can do a quick job without messing with setting up a level on a tripod.

To use a Locke level you use two sticks/poles. One to put the Locke level on while you're looking through it and another that an assistant holds that is used as the target for the Locke level. You'll measure the length of the pole the Locke level sets on. Let's say that's 60". Your assistant carries the other pole up the hill while you're looking throuh the Locke level until the bottom of their pole touching the ground is visible through the Locke level.

Both poles need to be held vertical for the best accuracy. Let's say the assistant slides a pencil along the pole they're holding until it lines up with the hairs in the Locke level. The pencil is say 6" from the bottom of the assistant's pole. That means that the difference in elevation between the spot where the pole with the Locke level on top is placed and the spot where the assistant's pole is located is 60" - 6" or 54". After writing that down, you move to where the assistant is and place the pole which the Locke level sets on exactly where the assistants pole was. Then the assistant moves farther up the hill and you repeat the process.

When you look through a Locke level you'll see a bubble level on one side that allows you to hold it level while you look through it.

By stepping up the hill you'll get a series of measurements that added together wil give you the elevation between your starting point and where your water supply should be for the pressure you want.

You can also use a length of clear plastic tubing filled with water since the water level will be the same at both ends. You could use that to determine changes in elevation by measuring the distance to the ground below the ends of the tubing. Make sure there's no bubbles of air in the tubing. Obviously the water can flow out the ends, but if you're careful and take your time you can do a good job.

-- Darren (, February 09, 2002.

John's right 1 psi pressure = 2.31 ft of head.

You can purchase a sight by viewing an object from start point to finish point while bubble in sight level is centered, you go to that point and sight again and again until you reach the finish point. You keep up with the number of sightings X your distance from eye ball to ground = total elevation head.

I guess if you could sight level, you could do an estimation of that way....

Renting a level might be safeiest.

Don't forget friction loss in the pipe if it is a long distance. Good Luck..

-- milam gerick (, February 09, 2002.

Thanks everyone. I don't understand alot of this but have printed it out for hubby (he will definately understand!). What is "friction loss"? The neighbors says his gravity feed system is 400 ft. up the mountainside from his house; ours will probably at least be comparable, I'm assuming, since our lands are relatively the same (his being a little steeper).

-- Lisa (, February 09, 2002.

Lisa, the pressure at the end of a pipe is less than the pressure at the beginning of the pipe because of the friction losses between the water and the pipe. If you do a search at for friction losses, you can find tables that list the losses for pipes of different sizes and different materials.

Over a long distance you may have to use a larger size pipe to get the pressure you want. With 400' of drop, if that's the case, you could have upwards of 150 psi with the right pipe size.

Is your neighbor tapping into a spring? If you haven't lived there very long you might want to check with others who have been about how well the springs flow during a drought. A household that's using a lot of water for running a washer, etc. may not have enough water.

If you do have a lot of water with a 400' drop you can generate your own electricity.

-- Darren (, February 10, 2002.

The neighbor laid 400 ft. of pipe down to his house on a gradually sloping property, not 400 ft of drop. He had to lay that much pipe in order to get proper water pressure. He said that he started with 2" pipe, then went to 1 1/2", and so on. Says he's got 50pounds of pressure. It is not a spring, but a drilled 250' well that he's got and so we are assuming that we will probably have about the same set up (of course, there will be variations, I'm sure).

Thanks for all the advice, guys. We will be going to the property soon (snow's melting finally!) to measure this out.

-- Lisa (, February 14, 2002.

Moderation questions? read the FAQ