Circular 1406 Understanding Water Quality Parameters for Citrus Irrigation and Drainage Systems 1 Brian J. Boman, P. Chris Wilson, and Esa A. Ontermaa 2 1. This document is Circular 1406, one of a series of the Agricultural and Biological Engineering Department, UF/IFAS Extension. Original publication date June 2002. Revised June 2015. Visit the EDIS website at http://edis.ifas.uf.edu. 2. Brian J. Boman, professor, Department of Agricultural and Biological Engineering, Indian River Research and Education Center; P. Chris Wilson, professor, Soil and Water Science Department; and Esa A. Ontermaa, agricultural consultant, Sebring, FL. UF/IFAS Extension, Gainesville, FL 32611. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or afliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension ofce. U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension. Introduction A basic knowledge of water quality is very useful for microirrigation system management and is an important consideration in the design and operation of the system. Terefore, the ability to read and understand a water quality analysis is important to the irrigation system manager. A careful analysis of the source water is prudent as a preliminary step to designing a microirrigation system. A microirrigation system requires good quality water free of all but the fnest suspended solids, and relatively free of dissolved solids such as iron, which may precipitate out and cause emitter plugging problems. Neglecting to analyze the quality of source water and provide adequate treatment is one of the most common reasons for the failure of microir- rigation systems to function properly. Obtaining a Water Sample It is important that a representative water sample be taken. If the source is a well, the sample should be collected afer the pump has run for approximately a half hour. When collecting samples from a surface water source such as a ditch, river, or reservoir, the samples should be taken near the center and below the water surface. Where surface water sources are subject to seasonal variations in quality, these sources should be sampled and analyzed at various times throughout the irrigation season. Glass or plastic containers are preferable for sample collection. For most analyses, the samples should be at least a pint. Te containers should be thoroughly cleaned and rinsed before use to avoid contamination of the water sample. Sample bottles should be flled completely to the top (with all air removed), carefully labeled, and tightly sealed. Samples should be sent immediately to a water testing laboratory. For a microirrigation suitability analysis, the following tests should be requested from the laboratory: Electrical conductivity (EC) or total dissolved solids (TDS), pH, calcium, iron, alkalinity, chloride, and if fltration information is needed, the quantity and size of suspended solids. Other parameters that are sometimes also needed to properly assess the suitability of the irrigation water are sodium, boron, potassium, manganese, nitrate, and sulfdes (hydrogen sulfde must be measured at the well head). Units Used in Water Analysis One obstacle in interpreting a water analysis is that water testing laboratories report results in various units. For example, the concentration of chemical constituents may be reported as parts per million (ppm), milligrams per liter (mg/L), or milliequivalents per liter (meq/L). A concentration reported in weight-per-weight is a dimen- sionless ratio and is independent of the system of weights and measures used in determining it. For many years,