Achyut Adhikari and Juan Moreira, Louisiana State University AgCenter School of Nutrition and Food Science

Water is an essential resource for small fruit growers, as it is crucial for irrigation and post-harvest activities. However, ensuring the microbial safety of water used in these processes is vital to minimize the risk of contamination and protect consumer health. The Food Safety Modernization Act (FSMA) Produce Safety Rule requires all agriculture water must be safe and of adequate sanitary quality for its intended use. Open surface water sources such as ponds, lakes, rivers, and collected rainwater are exposed to the environment and susceptible to microbial contamination. In this article, we will provide an overview of various options available to commercial small fruit growers, as well as other measures to improve water quality.

Practices to minimize microbial contamination such as vegetative filter strips, diversion ditches, avoiding animal access to water sources, and water treatment are effective in reducing microbial risk. In addition, growers can explore two other corrective measures to reduce the microbial risk to produce irrigation with contaminated water. The first measure involves establishing time intervals between irrigation and harvest to allow bacteria to naturally die off from fruit surfaces. This can help reduce microbial load and minimize contamination risks. The second measure involves regularly inspecting irrigation systems to maintain optimal conditions and identify any repairs needed. By ensuring the proper functioning of irrigation systems, growers can prevent potential sources of contamination.

If these corrective measures are not sufficient to reduce the microbial load present in the field to an acceptable level, growers have several options for water treatment that can significantly reduce microbial risks. Treatment options are divided into chemical and non-chemical treatments. It is important to note that any chemical method applied must be approved by the Environmental Protection Agency (EPA) and used according to the guidelines specified on the product label.

One of the most common and readily available chemical treatment options is chlorination. Chlorine-based compounds, such as chlorine gas or sodium hypochlorite, are added to the irrigation system to disinfect the water. Chlorine is effective for killing or inactivating a wide range of harmful microorganisms, including bacteria and viruses. Small fruit growers can use chlorine tablets or solutions following EPA guidelines to achieve the desired chlorine concentrations for effective water treatment. However, it is important to monitor chlorine levels regularly and maintain them within the appropriate range to ensure effective disinfection without negatively impacting plants or fruit quality. Any residual chlorine in the irrigation water can negatively affect the beneficial microflora of the soil.

Non-chemical treatments for water sources involve the use of physical methods that have been scientifically proven to reduce microbial risks. These treatments include ozonation units, ultraviolet (UV) light systems, and filter systems. Ozonation is an effective method commonly used in the agricultural industry. It involves injecting ozone, a powerful oxidizing agent, into the water supply. Ozone rapidly kills bacteria, viruses, and other microorganisms by breaking down their cellular structures. One advantage of ozone treatment is that it does not leave any chemical residues, making it an environmentally friendly option. However, small fruit growers should consider the cost and complexity of ozonation systems before implementation.

UV disinfection is another non-chemical method that utilizes UV light to kill microorganisms. UV radiation damages the genetic material of bacteria, viruses, and parasites, rendering them unable to multiply. UV disinfection systems are easy to install and require minimal maintenance. However, growers must follow scientifically validated UV methods with specific light sources, application times, and water turbidity requirements to ensure an appropriate UV dose for microbial inactivation.

Filtration is a water treatment method that removes particles, sediment, and microorganisms through a porous medium. Small fruit growers can choose from various filtration options, including sand filters, cartridge filters, and membrane filtration. Filtration helps in reducing the microbial load but may not eliminate all microorganisms. The selection of the filtration system should be based on specific water quality requirements and the operational capacity of the grower. Reverse osmosis (RO) is an advanced filtration process that effectively removes dissolved solids, contaminants, and microorganisms from water. RO systems use a semipermeable membrane to separate impurities from the water, producing high-quality, purified water. RO can be an excellent option for small fruit growers who need to treat water with high mineral content or specific contaminants. However, it is important to note that RO systems can have a higher initial cost and require regular maintenance.

Before exploring specific water treatment options, it is essential for growers to understand the importance of preventive practices in maintaining water quality. Implementing good agricultural practices, such as proper sanitation, reducing potential contamination sources, and regular monitoring, can significantly reduce microbial risks. In addition to the treatment options mentioned above, small fruit growers should regularly monitor water quality through testing. If any changes in the microbial quality of the irrigation water are detected, prompt actions can be taken to address the issue. Conducting microbial analysis and water quality tests can provide valuable insights into the effectiveness of the chosen treatment methods and enable growers to make necessary adjustments.

Furthermore, if treatment methods prove to be costly or ineffective over time, growers should consider the possibility of changing their water source. Choosing a clean and reliable water source can significantly reduce the need for extensive treatment. Surface water sources, such as ponds or rivers, are more prone to microbial contamination. On the other hand, groundwater often has better microbial water quality compared to sources exposed to the environment. Municipal water is the safest source of water due to proper water treatment applied by municipal authorities, although this may not always be a viable option for growers.

Dr. Adhikari from LSU AgCenter giving a demonstration of different water treatment systems using a mobile water treatment unit. (Photo by Juan Moreira)
Dr. Adhikari from LSU AgCenter giving a demonstration of different water treatment systems using a mobile water treatment unit. (Photo by Juan Moreira)