Understanding the basics of electricity by thinking of it as water

“We believe that electricity exists because the electric company keeps sending us bills for it. But we cannot figure out how it travels inside wires.” — Dave Barry

The fundamental laws of electricity are mathematically complex. But using water as an analogy offers an easy way to gain a basic understanding.

Electricity 101 – Voltage, Current, and Resistance

The three most basic components of electricity are voltage, current, and resistance.

  • VOLTAGE is like the pressure that pushes water through the hose. It is measured in volts (V).
  • CURRENT is like the diameter of the hose. The wider it is, the more water will flow through. It is measured in amps (I or A).
  • RESISTANCE is like sand in the hose that slows down the water flow. It is measured in ohms (R or Ω).

an image showing voltage, current, and resistance using a water hose as an analogy

Voltage, current, and resistance are all related. If you change one of them in a circuit, the others will change, too. Specifically, voltage is equal to current multiplied by resistance (V = I x R). Thinking about water, if you add sand into the hose and keep the pressure the same, it’s like reducing the diameter of the hose… less water will flow.

an image showing the relationship between voltage, current and resistance (V=I*R) using water as an analogy

Electricity 201 – DC, AC, Batteries, and Transformers

How does electricity work in electronics and the grid?

DIRECT CURRENT or DC is similar to the normal flow of water in a hose – it flows in one direction, from the source to the end. Historically, DC was originally championed by Thomas Edison in the famous Current Wars of the late 1800s. DC lost the war for the grid but it has found an even more exciting role in modern electronics like computers, phones, and televisions.

ALTERNATING CURRENT or AC is like the water flowing back and forth within the hose many times per second. The water analogy breaks down a little here but AC is easily created by electric generators (also called alternators). Nikola Tesla and George Westinghouse championed AC over DC and they eventually prevailed. AC is now the global standard for delivering electricity to homes and buildings via the grid.

an image showing alternative current AC compared to direct current DC using a water hose as an analogy

BATTERIES can be thought of as water pumps that circulate water through a hose that travels in a closed loop back to the battery. There are many metrics used for the capacity of batteries and not all are immediately logical. They include amp-hours and kilowatt hours. Batteries can only generate DC power.

TRANSFORMERS are like holding your thumb partially over the end of the hose to get the water to spray farther. The water volume (power) remains the same but the pressure (voltage) increases as the diameter (current) decreases. This is exactly what transformers do for overhead powerlines. The electricity can travel farther with fewer losses because the resistance (sand) doesn’t impede the electricity (water) when the current is lower (smaller diameter hose). Transformers only work with AC. The ability to move electricity over long distances is the main reason AC beat out DC a century ago.

Electricity 301 – Power and Energy

Now, let’s keep using the hose analogy to dive into the murkier waters of circuits (pun intended, sorry).

POWER is like the volume of water that is flowing from the hose, given a specific pressure and diameter. Electric power is measured in watts (W). And larger systems are measured in kilowatts (1 KW = 1000 watts) or megawatts (1 MW = 1,000,000 watts).

ENERGY is like measuring the volume of water that has flowed through the hose over a period of time, like filling a 5 gallon bucket in a minute. Electric energy is often confused with electric power but they are two different things – power measures capacity and energy measures delivery. Electric energy is measured in watt hours (wh) but most people are more familiar with the measurement on their electric bills, kilowatt hours (1 kWh = 1,000 watt hours). Electric utilities work at a larger scale and will commonly use megawatt hours (1 MWh = 1,000 kWh).

an image showing electric power compared to electric energy using a water hose as an analogy

Hopefully, this offers a helpful introduction to the basics of electricity. We’d love to hear your feedback and suggestions, so please leave suggestions and comments below.


23 thoughts on “Understanding the basics of electricity by thinking of it as water

  1. This is a great explanation. I wish my physics classes had used this in my undergraduate degree. As a mechanical engineer, this is more intuitive to me. Thanks!

  2. This is good learning exposure by understanding basic knowledge about electric power for those who has different technical background. Thanks.

  3. An important refinement of the concept presented in the sentence: “Transformers only work with AC” follows.
    A transformer, handling square wave AC, together with a number of fast, inexpensive electronic switches, can do for DC, what a simple transformer does for AC. This combination circuit is smaller, lighter, and less expensive, than the sine wave AC transformer that it displaces. Before fast cheap electronic switches, An AC transformer immediately followed the fuse and power switch in all high quality electronic instruments, like radios and TV sets. Now, all of those transformers are gone, because creating numerous new DC voltage levels is cheaper and easier, using switching circuits.
    Your article fails to mention that really serious, modern power lines, for many megawatts over hundreds of miles, like the Pacific Intertie, revert to DC to avoid skin effect losses, and losses due to imperfect, and expensive, power factor correction circuits.
    My hope is that underdeveloped countries will never need to interpose the difficulties of sine wave AC, between their solar, and fuel cell DC sources, and their LED and other DC loads.

    Free electrical energy from sine waves, while freeing it from the utilities that employ them!

  4. Thanks for your explanation. Having little knowledge of electricity, I have tried to liken the basics to waterflow in my minds eye. This analogy has defined that concept so well. It shows simplicity can sometimes be actually simple.

    1. Thanks a bunch for sharing the thoughts I had never seen this Wikipedia article. FWIW, I initially wrote this as you describe but when I expanded the article to include power and energy, I had to modify the analogy to differentiate between current and energy.

  5. Thank you Bill for the article, It was fun reading it and easy to understand, as mentioned above by another reader, if these concepts were thought in school, it would have been very easy to grasp – Thank you once again.

  6. In the simplified water & hose analogy for understanding how electricity works, where do WATTS come in? I still
    don’t have a completely clear picture. Thx.

  7. Loved The analogy! Now I can see this in my head, and understand what’s happening. Much appreciated! Now, when you have a 2000watt inverter in a RV, how do you figure out how long that will last with 120 volt appliances (ie: lights, tv, coffee pot, & refrigerator). How do you compute that?

    1. Watts are a measure of instantaneous electricity so a 2000W inverter only tells you how BIG of an appliance it can run but it doesn’t say anything about how long it can run that appliance. Most appliances will have their wattage in the instruction manual so you should be able to figure out which combination of appliances would exceed the inverter’s capacity and cause its circuit breaker or fuse to blow. Hope this helps.

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