In Internal combustion engines, water injection, also known as anti-detonant injection, is spraying water into the cylinder or incoming fuel-air mixture to cool the combustion chamber of the engine, allowing for greater compression ratios and largely eliminating the problem of engine knocking. This effectively reduces the air intake temperature in the combustion chamber. The reduction of the air intake temperature allows for more aggressive ignition timing to be employed, which increases the power output of the engine. Depending on the engine, improvement in power and fuel efficiency can also be obtained solely by injecting water. Water injection may also reduce NOx or carbon monoxide emissions. The purpose of this experiment is to investigate the effect of water injection on the engine performance, exhaust gas temperature and exhaust gas emission of a SI engine, water is injected in controlled quantities with the compressed air. Single cylinder, four stroke, air cooled type, 110 cc petrol engines used in the experiment. Obtained data will compare to calculate performance of specific fuel consumption, will get without a water supply to a petrol engine on the basis of performance. Performance test is conducted to find the fuel efficiency and is compared with conventional engine also emission is to be carried out to find Carbon monoxide emissions.