Water is essential for any living object to carry out its life functions. Tobacco is not an exception to this fact. Either deficiency or excess of water acts negatively on the quality of tobacco. Optimum water ensures high yields and good quality. More so in the later instance. Tobacco is cultivated as a rainfed, semi rainfed and irrigated crop in different zones of the world. Generally irrigations are carried out on an adhoc basis. Following a systematic schedule helps not only in saving precious water, but also in improving quality. By following IW/CPE (irrigation water given / cumulative pan evaporation) ratio, one can arrive at the time of irrigation. After assessing the field capacity of soil, optimum IW/CPE ratio for each crop phase of tobacco has to be worked out. With the help of field capacity, the quantum of water (in cubic meters) to be applied for each irrigation has to be calculated. According the depth of water to be applied in the field in to the furrow for a limited number of plants (say 20 plants) has to be established. In the case of overhead irrigation it is much simpler to use a rain gauge. As per IW/CPE ratio, the irrigation can be given for each crop phase as per estimated quantity of water and reduce the wastage and unnecessary excess watering to the crop. In India, this is further transferred to a simple "can" which is supplied to the farmer. This is popularly referred as "can evaporimeter". The evaporation is calibrated by noting the water evaporated in the can to the standard USDA evaporimeter. As per IW/CPE ratio, the number of irrigations to be given in each phase is calculated. Accordingly a coloured line is marked inside the can to help the farmer understand that he has to give an irrigation (which is a fixed quantum of water as per field capacity). For early phase of crop growth a red line is marked inside the can evaporimeter which is equivalent to 0.5 IW/CPE ratio. Depending on weather conditions, the farmer gives one or two irrigations during this period. When the plant enters full growth period the farmer is advised to give three numbers of green line irrigations (the green line is drawn taking IW/CPE ratio of 1.0). After three green line irrigations, the farmer is advised to give 2 or 3 yellow line irrigations which is again marked inside the can. This is equivalent to 0.7 of IW/CPE ratio. The farmer very easily follows the evaporation inside the can and as advised gives 2 irrigations in the first phase as the water inside the evaporimeter reaches red line and three green line irrigations and 2 to 3 yellow line irrigations (as per weather conditions) after topping and completes his crop. The total amount of water given varies from 280 to 320 mm to the soils which are sands/loamy sands and tobacco is cultivated at very high temperatures of 34°C. Since the farmer uses this simple technique of signals given by the can evaporimeter (marked inside), the irrigation system is referred to as "Signalling method of irrigation". This simple technology is highly useful to the farmer of many developing nations and also in places where water is scarce.