Here is some info that may clear up some myths about it:

What is water injection?

Water injection is a technology that is nearly as old as the car itself. However, like many automotive technologies, it has waxed and waned as fashion has dictated. Water injection has the ability to suppress detonation, allowing the use of higher cylinder pressures. It is easy to control and relatively simple to install. In times of tight emission controls, decreasing fuel octane and rising petrol costs, water injection is one of the best ways of controlling detonation. And it has another major advantage over taking other approaches - the 'fuel' is available at almost zero cost!

How it Works

Water injection is used to suppress detonation. Detonation occurs when the flame front does not burn progressively across the combustion chamber but instead explodes into action. This causes a massive and sharp increase in combustion pressures which can damage pistons, rings and even heads. Detonation can sometimes be heard as a 'tink, tink' sound coming from the engine. The piston and head shown here has suffered severely from detonation.

Water injection works in three ways. Firstly, when the water is injected into the intake system prior to the cylinder head, the small droplets absorb heat from the intake air. Water has a very high specific heat rating (it can absorb lots of energy while only slowly increasing in temperature) and so the intake air is initially cooled. Next, the small drops of water start to evaporate. Water has a very high latent heat of evaporation (its change of state absorbs a lot of heat) and so the intake air charge is cooled still further. Finally, when the remaining water droplets and water vapour reach the combustion chamber, steam is produced. This acts as an anti-detonant and also keeps the interior of the engine very clean, so preventing the build-up of carbon "hot spots".

Water injection was first experimented with in the 1930s. At the time it was discovered that detonation could initially be prevented by enriching the air/fuel ratio. As cylinder pressures rose still further and that approach ceased being effective, the injection of water into the intake air stream was found to prevent detonation. Interestingly, the detonation remained suppressed, even if the air/fuel ratio was then leaned-out. This occurred because the excess fuel was being used to cool the combustion process. When water replaced fuel in performing this function, less fuel was then required.

This has major implications for both emissions and fuel economy at high engine loads. In fact Saab on some of their recent turbocharged cars has used water injection at high loads in conjunction with leaner air/fuel ratios to reduce emissions output and improve fuel consumption. To put this another way, at high engine loads it is possible to reduce the amount of fuel being used, replacing it with water without sustaining any loss of power!

--excerpt from autospeed.
So what is alky and methanol injection relate to water injection?

well they are the same , the diffrence is the type of liquids used on the resovoir.

Methanol has ability to act as a secondary fuel as well as a very fast cooling agent, problem is that 100% methanol is very expensive and its not feasable to run every day

Alky , is a type of alchohol used primarly to decrease the temperatures of the charged air , although cheaper than methanol , it will vaporize a lot faster than methanol or water thus not having the same level of efficiency in cleaning your motor and preventing detonation.