can cars use water for fuel

[OElisa]

No, you cannot use plain water as fuel in a standard car. Water is not combustible; it's actually the result of combustion (H₂O). Pouring water into your gas tank will not create power—it will cause severe and expensive damage to your engine. The concept often comes from confusing water with advanced technologies like hydrogen fuel cells. These systems use hydrogen gas, which can be extracted from water through a process called electrolysis, but this requires significant external energy. The car itself does not run on water.

The idea of a "water-powered car" is a persistent myth because water molecules contain hydrogen, a highly flammable element. However, breaking the strong chemical bonds between hydrogen and oxygen atoms in water requires more energy than you would get back from burning the hydrogen. This fundamental principle of physics makes it impossible for an internal combustion engine to use water as a fuel source.

If water is introduced into your fuel system, it can lead to hydro-lock, where the incompressible water causes the engine's pistons to stop abruptly, potentially bending connecting rods and cracking the engine block. It also causes rust and corrosion within the fuel tank, lines, and injectors.

The legitimate technology that involves water is hydrogen fuel. A hydrogen fuel cell vehicle uses compressed hydrogen gas from a fueling station. Inside the fuel cell, hydrogen combines with oxygen from the air to create electricity, which powers the motor, and the only tailpipe emission is water vapor. However, the hydrogen is produced off-board, typically using natural gas or renewable energy, not directly from a tank of water in the car.

Fuel Type	Energy Source	How it Works in a Car	Tailpipe Emissions
Gasoline/Diesel	Chemical energy in fossil fuels	Combusted in an internal combustion engine	CO₂, NOx, particulate matter
Water	N/A (Not a fuel)	Causes engine failure; not combustible	N/A
Hydrogen (Fuel Cell)	Compressed hydrogen gas	Electrochemical reaction in a fuel cell produces electricity	Water vapor
Battery Electric	Electricity stored in a battery	Powers an electric motor directly	Zero (at the vehicle)

[DelTheo]

Look, as a mechanic, I've seen the results of this myth. Someone puts water in their gas tank trying to be clever, and next thing you know, their car is in my shop with a ruined engine. Water doesn't burn. It sinks to the bottom of the fuel tank, gets sucked into the engine, and because it can't be compressed like a fuel-air mixture, it literally seizes the engine. It's a surefire way to turn your car into a very expensive paperweight. Stick to the fuel listed in your owner's manual.

[SadieDella]

It’s a fascinating thought, but it misunderstands basic chemistry. Water is H₂O—it's what you get after hydrogen burns. To get energy out, you'd first have to break the water apart, which takes a huge amount of energy. It's like wanting to use ashes to start a fire. The hydrogen fuel cells you hear about are the real deal, but they start with pure, pre-made hydrogen gas, not a tank of tap water. The water is the waste product, not the fuel.

[SanAdam]

While the dream of fueling your car with water is appealing, the reality is all about energy density. Gasoline packs a massive amount of energy into a small volume. Water holds zero chemical energy we can use for combustion. The closest thing is hydrogen, which has great energy density by weight, but storing it is a challenge. So, no, water won't work. The research is in making hydrogen production cheaper and greener, not in making engines that magically run on water.

[McKimberly]

From a purely practical standpoint, using water for fuel is not feasible. The infrastructure doesn't exist, and the science isn't there for a consumer vehicle. If it were possible, every major automaker would be pursuing it relentlessly. Instead, billions are being invested in battery-electric and hydrogen fuel cell technology. These are the proven, scalable paths forward. The water fuel idea is a distraction from the real technological advancements that are actually changing how we drive.