# Why do I have low water pressure at the house from a tank located 100 feet up?

I have a new 1000 gallon tank at 100 feet above my house. There is about 300 feet of 2 inch hose from the tank to my house. I have a small creek filling the tank about 600 feet away. The flow into the tank is about 2-3 gallons a minute. The water line from the creek to the tank has a hill in the middle, but still fills the tank. Right now the tank is full, the water pressure at the house from the 2 inch hose going into 3/4 inch PEX is only about 15psi. I have a flow rate of about 7 GPM at the house.

Is there a potential that the line from the creek is holding up the water from the tank to the house? What else could be holding up the water? I have walked the installation, everything is buried 3 feet down. If there was a break in the line, wouldn't the water be dirty? It is crystal clear.

Thanks for the questions and clarity.

• Tank should be full or is full? Check if not sure. Do you have filters and are they clean? Commented Nov 17, 2023 at 23:14
• Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
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Commented Nov 18, 2023 at 0:23
• Have you done the walking yet? You need to know if water is getting into the tank and what the level is. "Should" should not be in your post. Commented Nov 18, 2023 at 9:28

If you have 100 feet of head, it is physically impossible not to have 50 PSI at the house when in-house flows are stopped. If the gauge is accurate, the 15 PSI reading tells you exactly where the top of water is: it is 30 feet above the gauge.

Run a faucet wide open for a minute, shut it, and check pressure again. If the gauge now reads lower, then most likely the tank is empty and the only column of water above you is what's left in the pipe. If the gauge still reads 15 PSI, you may have a large pipe break in the tank at the "30' above the gauge" point.

Right now the tank should be full

"Should"? You haven't walked the plant?

Understand that when you have a custom setup like this, it imputes upon you (or the person you hire) a certain responsibility to be familiar with the system, do regular inspections, and keep pathways clear to do that.

This situation should absolutely trigger a physical inspection of the system. Walk the pipe up to the tank, check the tank. If it's not full, check the pipe from the creek.

• I'm pretty confident that he actually has about 35 ft of head. See diy.stackexchange.com/questions/287148/…. In the comments from that question, he mentions that he has been getting 7.1 GPM from this system. Commented Nov 19, 2023 at 8:56
• @popham I was assuming this was static pressure with no flow. Commented Nov 19, 2023 at 18:25
• From comments on the duplicate question, he used a "My Elevation" app to find his tank height. From its docs, it looks like it maps GPS coordinates to a database of elevation information. It has good reviews, but I doubt that it would be immediately obvious to users if it was inaccurate. Does it interpolate grid data? Take the value of a closest grid point? How dense is the grid? (Those are rhetorical questions.) Commented Nov 19, 2023 at 20:05
• I am fairly confident that the my elevation app is not very accurate. Gave me completely different readings today. Commented Nov 20, 2023 at 5:38
• I will use the accurate altimeter tomorrow to see if it gives me better heights. Commented Nov 20, 2023 at 5:42

Assuming 350 ft of 2" PVC pipe, 20 ft of 3/4" PEX pipe (to the point where you measured the flow rate), and 35 ft of head (from your 15 psi), I compute a flow rate between 5.0 GPM and 5.1 GPM for your system. This is close enough to your 7.1 GPM that I believe that your pressure measurement is correct and that your elevation measurement was incorrect.

To compute the 5.0 GPM to 5.1 GPM theoretic flow rate, I used the Williams & Hazen formula from https://pvcpipesupplies.com/media/documents/engineering_design_data.pdf and I used a chart from https://mrpexsystems.com/wp-content/uploads/2016/08/17-Pressure-Drop-Charts.pdf.

To do the calculation, you hypothesize a flow rate, find the associated head losses from the cited sources, compute the orifice velocity using Bernoulli's equation (algebraically it reduces to v = sqrt(2gh) = sqrt(2(32.2ft/s²)(35ft - head loss))), and multiply orifice velocity by the orifice's cross sectional area to get a flow rate. You iterate this process until the hypothesized flow rate agrees with the computed flow rate.

7.1 GPM is a nice flow rate. As long as you're in spec for any mechanical equipment, it shouldn't bother you.

• The big challenge that is there is that the psi has increased by 1 pound today to 16. I am not sure how this was accomplished. There is good flow rate and I keep hoping it is an airlock that will work it's way out Commented Nov 20, 2023 at 5:40
• The boiler needs a psi of 20 to start to work. Commented Nov 20, 2023 at 5:41
• @John, you mentioned a hill in the line from the creek to your tank. Are there similar humps in the tank-to-house line? You can check your elevation at apps.nationalmap.gov/viewer. You click on the icon with the `XY` for polling elevations. There's another icon that looks like a stack of 3 sheets of paper for layers. Under layers, turn on the "Imagery (NAIP Plus)" layer for a satellite image overlay. Commented Nov 20, 2023 at 6:47
• @John, following article.sapub.org/10.5923.j.ijhe.20180703.02.html, I compute an air clearing velocity of 3.5 ft/s versus your 7 GPM flow rate's velocity of 0.7 ft/s in the 2" line. The air clearing velocity is predicated on a slope of 100 ft of fall per 350 ft of line. For air lock related head losses, the air's total height is roughly equal to its head loss. That's 65ft in your case. Good source: www2.gov.bc.ca/assets/gov/…. Commented Nov 20, 2023 at 8:04
• I just had the water running for an hour with the tank lid off. Water pressure dropped to 12 Commented Nov 20, 2023 at 22:12

I think that you were all right in my opinion and I apologize for taking so long to respond. I do have an answer. There was a vacuum or air lock in the pipe and it required a pump to pump it out due to the length of the line. 400 feet of line needed to be cleared of air. It is now clear and I get a pressure of 35 psi, near what we discussed