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How To Estimate Agricultural Water Withdrawal

When registering water withdrawal (which applies to groundwater or surface water), agricultural irrigators may report a direct measurement of water use or an estimation of water use. While measurement is preferred, irrigators without meters may estimate water withdrawals based on the number of acres irrigated and the depth of water applied (inches) per irrigation. This page describes the "acre-inches" estimation method. Other methods for estimating water use described in the Great Lakes Basin Water Withdrawal Registration Handbook are also allowed.

Non-agricultural irrigators, such as golf course operators, may also use these estimation methods. However, unlike agricultural irrigators, they must comply with the two-year advance registration requirement.

Using the Agricultural Water Withdrawals worksheet

The worksheet titled "How to Estimate Agricultural Water Withdrawals" (PDF file, 511 kb) contains a record keeping and computation form to help keep track of water use. Use of this form is voluntary. However it is a useful method for determining the need for registration.

Only the official Water Withdrawal Reporting Form for Agricultural Facilities is required to be submitted to DEC. That form can be found on the Agricultural Water Withdrawal page.


Registration is required if water use in any 30-day period exceeds 3 million gallons. This is equal to 110.5 acre-inches per 30 days or a daily average water use of 100,000 gallons (3.7 acre-inches). A 30-day running total record of the days that irrigation took place and the amount of water applied per acre will help determine the need for registration.

If water users are certain of registration, they can skip the 30-day running total and report the total water use by calendar month. If irrigation lasts longer than one day, water applied must be divided into daily proportions for the following reasons:

  • The law requires reporting the amounts of water withdrawn and lost during each calendar month. If an irrigation period overlaps two months, the water used in the period must be pro-rated into two parts - one for each month.
  • If it is uncertain whether withdrawals will exceed 3 million gallons (110. 5 acre-inches) in any 30-day period, irrigators will need to keep a running total of water used in the most recent 30 days. Thus, daily water use must be calculated for the 30-day running total.

Table 1 shows how to calculate the number of irrigation periods needed to exceed the reporting limit for a one inch application depth on fields of various sizes. The first column shows acreage for five irrigated areas, ranging from 10 to 100 acres. Fill in the desired application depth in column two. For the purposes of Table 1, a one inch application depth is chosen. If the application depth is other than one inch, the second column should be changed as required. The acre-inches of water applied per period can be calculated as the product of columns one and two as shown in column three. The fourth column is a conversion of acre-inches to gallons. The last column shows the number of time periods needed to reach the 3 million gallon threshold. If a farm has many irrigated fields, the water use must be calculated for each field. If the sum of water used on all fields exceeds 110.5 acre-inches in any 30-day period, registration is required.


Table 1 shows that a farm of 100 acres (see bold row) applying 1.0 inch of water uses 100 acre-inches of water per period of use, or 2,715,000 gallons of water. The 1.1 in the last column indicates that if more than one irrigation period falls within a 30-day time period, the irrigator will exceed the 3 million gallon threshold and, therefore, must register.

Table 1: Water withdrawal calculation for a 1.0 inch application depth.
Water applied
per period in
Gallons Period to reach 3
million gallons or
110.5 acre-inches
10 1.0 10 271,500 11.0
25 1.0 25 678,750 4.4
50 1.0 50 1,357,500 2.2
75 1.0 75 2,036,250 1.4
100 1.0 100 2,715,000 1.2

For Additional Help

Additional help in estimating water withdrawals or completing registration forms can be obtained by contacting:

New York State Department of Environmental Conservation
Bureau of Water Resource Management
625 Broadway
Albany, New York 12233-3508
Telephone (518) 402-8182

This web page was prepared from a handbook developed with the assistance of the New York State Water Resources Institute and Cornell Cooperative Extension.

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