MAILBOX: Water Pressure

Intermediate
A simple water pressure system.
This simple pressure system provides “city” pressure reliably, and at much lower cost and complexity than an elevated tank. The pump with integrated pressure switch and the pressure tank can be scaled up to match the water demand.
A simple water pressure system.

I just read the water pumping Q&A in “Ask the Experts” (HP163), where an expert addressed Jim Yannaccone’s questions about several water pumping issues.

There was a lot of good advice in the article, but it brought to mind an issue that’s bugged me for years: Why do we seem to need such high pressures in our water systems? High pressure equals high pumping costs, and that equals more expensive pumps and more solar-electric modules.

Most of us have seen old farmhouses with attached water towers. Often these were only 20 to 30 feet high, meaning the head, when the tank was near empty, was only going to be as little as 5 to 15 feet at a shower nozzle. This is only about 2 to 8 pounds per square inch (psi).

It seems like that would make showering impossible, but it does not. I lived for 20 years with no pump, relying on gravity to pressurize my water system. The water source was a spring, and it was located lower than the peak of my roof—the pressure was only 2 to 3 psi. I was still able to have a great shower. Here’s how:

To reduce pipe friction, I used 1-inch main lines, and 3/4-inch lines to the shower. I figured I wouldn’t get a decent flow at the shower if I used a “modern” washerless shower control, because they have tiny orifices. I used an old-style shower control—the kind that used rubber washers. I picked the one with the largest orifice I could find.

The disadvantage to showering with low water pressure was that if someone ran water in a sink or flushed the toilet while someone else was showering, they would hear very loud shouting or screaming coming from the shower!

I suggest using an elevated storage tank instead of relying on a pressure tank. A 40-gallon pressure tank will only provide about 12 gallons of water with a 30 to 50 psi pressure switch setting. If you’re able to run your home on 2 psi, that same tank would provide almost 40 gallons of water, but that’s usually not nearly enough to keep you in water.

You can place a 500-, 1,000-, or even 2,500-gallon tank on land that’s only 5 to 10 feet higher than your highest showerhead—this is much more likely to be available than the 100 feet suggested in the recent “Ask the Experts” response. This would provide you water for days or weeks when the sun isn’t shining. If you don’t have that much elevation available, consider building a water tower. Even if you only stick a fairly small tank up there, you’ll be way better off than simply using a standard pressure tank setup.

Malcolm Drake • Grants Pass, Oregon

You are correct that standard water pressure used in the United States is far higher than necessary for simple water delivery. One reason for this is fire protection. Fire hydrants are connected to municipal water mains, and require high pressure to supply fire hoses. Pressure regulators are then used to reduce pressure where needed, but there is no energy to be saved there, because it has already been spent to produce the main pressure. High pressure allows use of smaller pipe sizes because the resulting pressure drop becomes relatively insignificant. Small pipe costs far less than large pipe, and is easier to fit into the walls of buildings.

Until the 1970s, most new construction used copper pipe, which is expensive. Energy was cheap then. It was cheaper to apply energy to overcome pipe resistance than it was to use larger-diameter pipes. Our water supply and plumbing standards reflect these factors, and they apply to private water systems, too. State and local codes call for a minimum pressure of 40 psi. You need 2.31 feet of elevation to produce 1 psi. So 40 psi requires nearly 100 feet of tank elevation!

A pressurizing system will cost much less than an elevated tank, and will weigh far less—the 500-gallon tank that you suggest would weigh more than 4,000 pounds! Another challenge to elevated tanks is freeze protection. If you travel south to warmer climates, you will find elevated tanks as you describe, often around roof level. The systems that work well use large, bulky pipes with ball valves and avoid restrictive fixtures. Traditional toilets and washing machines fill more slowly, but will function fine. However, dishwashers will not function, nor will sprinklers, hose sprayers, or tankless water heaters. A greater amount of water will be needed to rinse hair. Owners of gravity systems often add a pressure booster pump to serve modern appliances and fixtures. This tends to conserve water, compensating for the modest energy used.

A water storage tank that is not pressurized must be open to the atmosphere. Air must be allowed in for water to flow out. This can draw in contaminants. State and local codes may require chemical disinfection for such “open” storage systems. A small tank will also get warm in the summer. This may be unpleasant at best, and may support growth of bacteria and algae.

In most situations, there are just too many problems and costs to recommend an elevated tank or other low-pressure gravity-fed water system to supply a simple low-tech household.

If you consider the big picture, a pressurizing system looks like a bargain.

You are correct to use large pipe to minimize pressure drop. Use one size larger than the minimum pipe sizes required by plumbing codes. Use PEX (flexible) pipes and other means to avoid sharp 90° elbows. Agree on this clearly—in writing—with your plumber. You will then be happy with a pressure range of 30 to 40 psi instead of the “normal” (wasteful) range of 40 to 60 psi.

Windy Dankoff • Founder (retired), Dankoff Solar Pumps

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