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Dec 10, 2023

Can You Really Pump Water Without Any Electricity?

Rhett Allain I'm surprised at the number of YouTube and TikTok videos showing

Rhett Allain

I'm surprised at the number of YouTube and TikTok videos showing novel ways to pump water, but I guess it makes sense, because the whole world pretty much runs on water. If you haven't seen these before, they often show someone sticking some pipes into water and shaking them back and forth until all of a sudden they start spouting endless quantities of liquid. It looks magical: There's no apparent power source, but the water keeps flowing, sometimes from an outdoor body of water, sometimes from a container the person keeps refilling. It's like these devices run on "free energy," or energy with no apparent origin.

Could you actually make a "free energy" water pump?

Physics spoiler alert: There are actually two methods to move water that don't require an external power source—but that's not the same thing as running on free energy.

The first method is the siphon pump. This one is pretty common and very easy to set up. Here's what you need for a simple demonstration: a glass of drinkable water and a bendy straw. Fill the glass almost to the top. Now bend the straw and put the short end into the glass with the longer part hanging over the rim. Here's how that should look:

Next, things are going to get just a little bit weird. Suck on the long part of the straw until water gets to the end. Then let go of that end while making sure it's lower than the level of the water in the glass. Hopefully you are outside or near a sink, because water will start pouring out of the end of the straw. That's it. You just made a siphon pump.

The water will continue to flow—and maybe make a mess on your kitchen counter—as long as these two conditions are true: The output end of the straw must be lower than the water level in the glass, and the input side must be underwater. Simple.

But how does this work? Here's an illustration of that setup, with the water running through the bent straw. Part of the straw is submerged in a glass of water and part is hanging over the edge, so the water can "fall" out of the free end.

Jeremy White

Kate Knibbs

Jeremy White

WIRED Staff

As a thought experiment, let's imagine that as the water flows out of the free end, it leaves behind a space that's nearly empty, except for perhaps a little bit of water vapor. With nothing in that part of the straw, the pressure there is very close to zero. Since pressure is defined as the force per unit area, a zero pressure means there is no force pushing up at the rest of the water in the straw.

Now let's go to the other end of the straw, the one in the cup of water. That part of the straw is underwater, and there is pressure that produces a force pushing the water up the straw. This pressure is due to a combination of two factors: the depth of the water (the deeper you go, the greater the pressure) and the atmospheric pressure from all the air above the surface of the water. But here's the important part: Since there is a force (from the total pressure) pushing the water up the straw, but there's zero pressure in that empty space, there is a net force on that bit of water which moves it up the straw towards the free end.

Of course, there's not really an empty space in the straw. That was just a thought experiment to show that when water falls out of the free end of the straw, it won't push back on the rest of the water. Once the water starts flowing out, it will just keep flowing.

It's also useful to see why the straw itself is important. It doesn't just guide the flow of water. It prevents air from getting inside, which would increase the pressure pushing back on the water and would stop it from flowing. To make this kind of pump work, you need a tube or pipe that is rigid and doesn't collapse due to the external atmospheric pressure. A simple plastic straw works fine for small amounts of water.

Jeremy White

Kate Knibbs

Jeremy White

WIRED Staff

There's one more thing to consider: Does a siphon pump create "free" energy, since it moves water without an external energy source?

Let's consider a siphon pump draining an elevated pond. (Remember, it has to be an elevated pond because the output end of the siphon pipe has to be lower than the input end.) Imagine that 1 kilogram of water gets pumped out of the pond. That water ends up somewhere lower than where it started—for this example, I'm going to say it ends up 1 meter lower. In terms of energy, this decrease in height means that it will also decrease in gravitational potential energy. We can even calculate this change (mass × g × h) to get a decrease of 9.8 joules.

The important part is that it decreased in energy. You don't need to add any energy to the system to lose energy—the water does that for you. It's not a "free energy" pump, it's a "losing energy" pump. For practical purposes, that's fine because it still lets us move the water without having to do any work.

Let's do a quick test to see if some of these online videos showing no-power pumps might be siphon pumps. (I’ll do one as an example, and you should be able to check out the others on your own.) Let's take this one of a person by a river with a fancy pump. They shake it back and forth to get it started, then water starts to flow out the end of a pipe. It looks something like this:

Could this be a siphon pump? The answer is no. Notice that the input end of the pump is lower than the output end—that means it can't be a siphon.

Let's explore another option: the ram pump, short for hydraulic ram pump. Basically, the ram pump is a way to move water to a higher location without an external energy source. This one is a bit more complicated, so I'm going to start with a diagram:

Jeremy White

Kate Knibbs

Jeremy White

WIRED Staff

In this case, water starts from a source that's higher than the pump. (That's important.) As this input water moves down from the source, it increases in speed and goes out the waste valve. However, this moving water causes check valve A to close, which stops the water from exiting. But since the water is moving into a closed valve, it is redirected up past the other check valve, B, and causes the air space to be compressed. Once the air is compressed, the water stops flowing and valve B closes. Once that valve closes, the compressed air acts like a spring to push the trapped water up the output pipe. Then the whole process starts over.

That's pretty complicated; it's tough to get the values adjusted so that the thing works correctly. So I'm not going to build a ram pump, but if you want to give it a go, here's a nice video showing one that really works. (Good luck.)

In the meantime, let me point out the key aspects of this pump. First, the pump is lower than the water source, but the output is higher than the water source. That might seem bizarre, but that's the way it is. Second, every time water is pumped to a higher level, some water is ejected from the pump—that's the wastewater.

OK, let's go back to the TikTok video. Could it be a ram pump? Remember that you need three levels for this kind of pump: The output is at the highest level, the water source is in the middle, and finally the pump is down below. If you don't have all three of these levels, you don't have a ram pump.

In the diagram I drew above, which is based on that video, the person is pumping water out of a river, which appears to be the source of the water. So this can't be a ram pump, because the water can't come straight out of the river. Remember, the pump must be at a lower level than the source. And in this case, the source, not the pump, is the lowest level of the system.

The other thing to look for is the wastewater. In a true ram pump, there should be extra water shooting out of the lower level. Without that, you don't have a ram pump. And in the video, there's no visible wastewater.

Well, then how could it work? Who knows. Maybe it's just an illusion. Maybe there's an electric pump submerged in the river and connected to the pipe. I tried messaging the person who posted the video and got no response.

The bigger question is, does a ram pump create free energy? It certainly seems that way, because you are moving water to a higher location. That would increase its gravitational potential energy, instead of moving it downwards and decreasing its potential.

But that's not really what happens. Let's imagine we have a working ram pump. Suppose I start with 20 kilograms of water at the source. There is a pipe going down 1 meter to a pump. After that, some of the water (let's say 10 kilograms) is pumped up to a height of 1 meter above the original source, so that it increases in gravitational potential energy. That means that only 10 kg of water was ejected as waste at the pump level—but since it moved down, it had a decrease in gravitational potential. Overall, with 10 kg going down 1 meter and 10 kg going up 1 meter, the net change in energy is … zero. The pump "pays" for the higher energy water at the output by letting water flow to a lower point.

Of course, in this example the pump would be 100 percent efficient—and that never happens. Energy is lost in the ejected water and in the friction between the water and the pipe.

And that leads us to one last problem: Even if you had an impossibly efficient generator that was powered by the falling water from the ram pump, it still wouldn't give you free energy. Since some of the water has to be ejected at the lower end, the water source would eventually dry up. That would mean you have to use energy to lift up more water to add to your source. Oh no! Now you’ve just lost your scheme for free energy.

In the end, both the siphon and ram pumps move water without any external energy input—but you don't get more energy than you started with. However, you might get water where you want it. And that's the point of a pump.

Update 3-27-2023 12:11 pm ET: This post was updated to correct the direction of check valve B in the ram pump diagram.