Water Injection

What is Water Injection?

Water is pumped under pressure through a very fine nozzle into the air flowing through the air intake. This water appears in the intake as a very fine mist.

What does it do?

A few things. The main reason it is used is to reduce the air intake temperatures to reduce the chances of detonation, as well as assisting performance.  One beneficial side effect is to also "clean" the intake valves and the combustion chamber.

How does it cool the air?

Water is an excellent coolant - it is used in your engine as a coolant and in your intercooler as a coolant. Water absorbs heat better than air. I believe it absorbs approx 4 times as much heat as air. As the water is sprayed into the air as a fine mist is absorbs some of the heat from the air and so cools the intake temperatures.

How much does it cool it by?

This depends on several factors namely temp of air, temp of water, amount of water you pump into the air flow...

Using a 0.5mm nozzle I have measured air intake temperatures as below:


Intake temperatures
Before WI With WI When
32 8 Winter
38 20 Spring
47 23 Summer


As you can see there is a substantial decrease in temperatures when running WI.

Note that these are "typical" temperatures, car with filter open to hot engine bay air and running 15psi boost on a hybrid turbo, IC heat wrapped and running a larger IC radiator. Ambient air temperatures affect the temperatures quite dramatically as shown above.

Where were these temperatures taken?

The were taken from inside the plenum chamber of the intake manifold, i.e. the bit just after the throttle body. They were taken with a digital temperature gizmo. Click here to find out more about the gizmo...

How do I get WI?

At the moment there really is only one manufacturer  - Aquamist. They sell a kit and it's pretty good. The kit consists of:

You can get the kit from loads of shops, check out the links section.

Where did you get yours from?

"Gatesgarth Racing Developments" will probably be the cheapest supplier - (01948) 841581 / (07971) 952084. Join the GT4OC and let him know and you will get a hefty discount - I got mine for under 300 delivered...

Is it any good?

Yep. All the bits you need are in the kit and probably some to spare! I didn't get a wiring diagram with mine but you can get this from Aquamist's website.

It also seems reliable, providing it is installed correctly and professionally.

Any drawbacks?

You will need to mount the WI nozzle somewhere. I would suggest drilling and tapping the throttle body. Be careful not to leave any metal deposits in the throttle body or it'll end in tears!

You'll need a water tank and a route to get the water from the tank to the pump.

You'll need to keep a regular check on the water storage tank and keep filling it up...frequency depends on size of your tank, size of nozzle fitted and how heavy your right foot is! My tank is 5l and I fill it up approx every 2 fuel fill ups - ish.

Don't run out of water cos it'll shorten the life of the pump and it'll make a horrible noise.

Watch out that water doesn't freeze in the pipes/pump during winter - you'll need a new pump!

What's your verdict?

Bloody marvellous bit of kit. Go and buy one!

You would be VERY hard pushed to find an intercooler to reduce intake temperatures as much as this!

Anything else?

You can buy uprated kits that can be mappable and do all sorts of fancy things. Personally I wouldn't bother with the added expense. Use the pressure sensor supplied and have it coming in a few psi below your maximum boost pressure.

There are other kits out there, (although few and far between), and as yet they have only just been put together, operation and reliability have yet to be established.

You can cheaply make your own system using boost pressure to force water through a fine nozzle...