How can I treat irrigation water to meet GAPs standards? Can I use river water?

Answer: The ATTRA publication An Illustrated Guide to Growing Safe Produce on Your Farm: Good Agricultural Practices introduces all the aspects of GAPs and has a great resource list. It’s available on our website at www.attra.ncat.org. More information can be found on the USDA’s website at www.ams.usda.gov/AMSv1.0/GAPGHPAuditVerificationProgram. For GAPs certification, surface water that is being used for overhead irrigation of crops should be tested to ensure that it meets the EPA’s coliform limits for recreational use of water. This standard is no more than 10,000 count per 100 ml in a single sample. Usually, a test is taken early in the season, another in mid-season, and another toward the end of the season. There are no set standards, but you might ask if this is the standard your GAPs auditor is using. If you have already done testing and it doesn’t meet this standard, then treatment might be necessary to meet GAPs standards. Using ultraviolet (UV) as a water treatment system for irrigation has its share of problems. First, there are large industrial-size systems and small household systems available, but the size you would need for a flow of 40 to 60 gallons per minute is hard to find. In addition to problems of availability, water from a river would need to be pre-filtered in order for UV treatment to be effective. You may also need to treat with chlorine in addition to pre-filtering and UV treatment because UV is not effective protection against viruses. That means three separate systems to do the job. As for coliform bacteria, UV treatment is not recommended for coliform above 1,000 counts/100 ml. For all these reasons, it doesn’t seem to be a practical solution for treating irrigation water to meat GAPs standards.According to Berry Hill Irrigation, there are chlorination treatment units that would handle lower flow rates. One is a Regal chlorinated filter that uses chlorine gas to treat the water. This filter costs about $1,200. However, chlorine gas can be very dangerous and, although plants need a minute amount of chlorine, this above system could possibly introduce levels of chlorine that would damage the plants.The proposed federal drinking water standard, from the Safe Drinking Water Act, for chlorine levels is 4 ppm. This is the limit for the use of chlorine in organic standards, as well. The effectiveness of the chlorine treatment is determined by the amount of organic matter in the water and the pH of the water. If you did decide to use a chlorine system, you may need to still pre-filter the river water to remove organic matter before the chlorine would be effective.There is also a hydrogen peroxide treatment system from a company called Flow Tek that requires a water sample to determine the level of hydrogen peroxide that is needed. Because chlorine and hydrogen peroxide are both restricted under organic standards, the use of a treatment system that used these materials would jeopardize organic certification for your farm. If organic certification is one of your goals, be sure to contact you certifying agent and ask if there is a treatment for your irrigation water that would meet his or her standards. (Note: The mention of specific products or companies does not constitute an endorsement by NCAT, the ATTRA program, or the USDA.)