Many factors influence the amount of water needed by plants. The Blaney-Criddle Method is a formula used to estimate water loss due to evapotranspiration in crops. At its simplest level, the calculation takes into consideration such factors as consumptive water use, mean monthly temperatures, and percentage of total annual daylight hours that were available over the period being measured. There are several other formulae employed to assess the amount of water plants need and it's an important aspect of the science of irrigation - whether in agriculture or for domestic and leisure purposes. Given the growing need to conserve water supplies and the increasing number of restrictions governing how much water we use for irrigation, knowing how much and when to water is a critical aspect of landscape management.