Yes it can be done if we have basic data related to cultivated land in a particular province (area), crops grown, system of irrigation (drip or sprinkler), water requirement of crop in each crop cycle/system, average of water needed each year can be worked out as a factor. This factor can be further used for multiplication with cultivated area. This will give an idea that how much water is used for irrigation. 

The state water agency and National Agricultural Statistics Survey (NASS) as well as USGS or university may have information, data or reports specific to your question.  The number of wells on agricultural lands, availability of surface and groundwater for use are questions to consider.  The riparian water rights in the eastern USA allows each landowner to use a reasonable amount of water from streams.  In addition, some farms may store surface water in ponds to help meet their water needs if surface waters and well water is marginal at dry times of the year.  So it may be difficult to generalize, and probably worth some contact with farm industry specific to the each area of interest.  Some farmers will rely heavily on irrigation and may use ET indicators to save water, others may irrigate on some schedule as they have abundant water, others dont have access to water and grow crops that will not normally need irrigation, and some without access to water will look at farmers almanac and decide which crops are most likely to survive.  To assume all farmers are the same and have similar needs on their farms may be a mistake.  Not all farms in a state the size of New York, have the same soils, rainfall, crops, access to surface or groundwater, size of operation, etc.  Start with an internet search, but likely various agencies as NASS, state water agency, farm industry, county soil and water conservation agencies, USDA-NRCS, USGS and State Climate agencies would have some information that either could be applied directly or could be developed.

Hello

By doing some super reforms of irrigation efficiency at least 20% increase. In this regard, water management improvement plan to promote the recovery and management Optimize water use in the process of production (wheat and corn) in the study conducted Mzrh The results were revealed in a wheat field in the water was about 29% savings. Irrigation and sprinkler irrigation systems and controls about 10 percent compared to 35 percent of the system Increased surface area. Ast.karayy water consumption for this product is about 40 percent The farm was increased. In a cornfield in the water was about 31% savings. Irrigation efficiency and water use efficiency of about 18 percent to about 27 percent from the field evidence to support this Product increased. This work was supported by the Ministry of Agriculture Organization of research, education and extension Agriculture and Natural Resources Research Center of Chaharmahal and Bakhtiari And Integrate management of agricultural extension has been redirected. Here is an article link.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj144_LurrPAhUFfhoKHQNfCrwQFggbMAA&url=http%3A%2F%2Fcharmahal.areo.ir%2F_charmahal%2Fdocuments%2F% 25D9% 2585% 25D8% 25B5% 25D8% 25B1% 25D9% 2581% 2520% 25D8% 25A8% 25D9% 2587% 25DB% 258C% 25D9% 2586% 25D9% 2587% 2520% 25D8% 25A2% 25D8% 25A8% 2520% 25D8% 25A7% 25D8% 25B3% 25D8% 25AA% 25D8% 25A7% 25D9% 2586.pdf & usg = AFQjCNEjc8HhZZc9mKtmITSn6dEIf6-TzA & bvm = bv.134495766, d.d2s

Thanks William. This is great information. I have been digging into NASS stats, but they only give total irrigated acres per county and I was hoping to try to figure out what types of crops the water is going to and where it is coming from.  I agree that it is wrong to treat all farms the same (having been born and bred in the heart of the Finger Lakes :). But we shall try our best. 

Thanks Suresh. This is very helpful. I think I need to get the crop coefficients (Kc) at different stages for different crops grown in NY State and am having trouble finding those. There are crop coefficients for many areas of the world, but not NY (or even the northeastern US as far as I can tell).