Maharashtra is one of the leading producers of cotton in India. But due to water scarcity the cotton production is fluctuating very much due reduced actual rainfall and consequently decrease in water table in each year. This study is conducted around northern Maharashtra region by collecting data for minimum and maximum climatic temperature and rainfall data of 2010-2016. To quantify the water need of cotton crop it is essential to calculate the Evapotranspiration potential using Blaney – Criddle equation and water deficiency ratio to consider the irregularity in deficiency as well as availability of rain water in this assured rainfall zone. The information about Water availability and deficiency in particular developing stage for crop will be very beneficial to suggest proper and correct irrigation supplements.