Summary: Irrigation water analysis only helps decide filtration, treatment and management when the sample represents the water that actually enters the system. This guide shows where and how to collect in dams, rivers and wells, what parameters to discuss with the laboratory to evaluate the system, soil and crop and how to interpret the report, without treating isolated numbers as a universal rule.
Why water analysis comes before the project (and not after the problem)
In localized irrigation, water passes through very small holes and labyrinths. Therefore, water quality matters as much as the available flow. Batista and collaborators (2008), in the magazine Engineering in Agriculture, show that sensitivity to clogging depends on the characteristics of the emitter and the physical, chemical and biological components of the water.
In practice, the report answers design and operational questions:
- Filtering: what type of filter and what degree of filtration the water requires (see the irrigation filters).
- Treatment: whether there is a need to oxidize iron, correct pH or control algae and bacteria.
- Maintenance: how often to wash filters and lines and when to do chemical cleaning.
- Fertigation: whether water can react with fertilizers and form precipitates.
Operating errors that lead to obstruction are in the article on clogging of drippers. Here the focus is prior: obtaining a reliable water diagnosis.
Before collecting: define the objective and agree with the laboratory
Embrapa Soils' technical manual on water collection for agricultural and environmental purposes deals with the collection plan before going to the field and reminds you to consider the time between collection and analysis. On rural properties, this translates into three decisions:
- What question do you want to answer. Evaluating a new source for a project is different from investigating clogging in an already working system. In the second case, it is also worth collecting at points in the system, and not just at the collection point.
- What parameters to order. Define the list with the laboratory and who will size the system (details in the next section).
- Bottle, conservation and shelf life. Each laboratory has its own requirements for vials, preservation and sample delivery times, depending on the parameter. Ask for these guidelines in writing before going into the field. Also ask if any parameters need to be measured on site.
As a general volume guideline, the Embrapa manual mentions 1 to 1.5 liters for most determinations. Confirm with the laboratory: the assay list may require other volumes and separate vials.
How to collect the sample from each type of source
Dams, reservoirs, rivers and streams
The Embrapa manual recommends choosing a representative point, away from stretches of standing water and banks. The steps below apply to physical-chemical collection in a preservative-free bottle, when authorized by the laboratory. Do not rinse sterile bottles intended for microbiology or bottles that already contain preservatives. For these tests, follow the specific procedure provided by the laboratory.
- If the laboratory advises the environment, rinse the preservative-free bottle three times with water from the collection point.
- For the manual collection described by Embrapa, immerse the bottle with the mouth down, approximately 15 to 30 centimeters below the surface, and then turn the opening against the current, slightly upwards, to allow water to enter and air to escape. Avoid the surface film and do not stir the bottom.
- Fill to the level indicated by the laboratory, close tightly and identify the bottle immediately.
For irrigation, extra care must be taken: try to collect close to the pump's collection point and at the same depth as the water intake, when possible. This way, the sample better represents the water entering the system. Extension guidelines from Utah State University and Auburn University reinforce that vial preparation is assay dependent and that collection must preserve sample representativeness.
Wells
In shallow and deep wells, stagnant water may not represent the source. Therefore, the Embrapa manual guides the removal of this water using a procedure appropriate to the characteristics of the well. In a well with a pump, let the water run before collection, in an outlet prior to filters or treatment, according to the purging criteria defined with the laboratory or technician responsible. The time depends on the well and the pump; This is not a recommendation to literally empty the well.
Inside the irrigation system
When the objective is to investigate clogging, compare samples from different points: intake, filter exit and end of a lateral line. A study published in the journal Rural Science (Ribeiro and Paterniani, 2008), using microsprinkler, analyzed the water from the catchment and sectors of the system. Dissolved iron in the ferrous form (Fe²⁺) can pass through the filtration and then oxidize, forming poorly soluble ferric compounds and precipitates that block the emitters. Therefore, clean-looking water at the filter outlet can still form deposits further down the line.
Identification, conservation and transport
Identify each bottle with the point and origin of the water, the date and time of collection and the name of the person who collected it, as instructed by Embrapa. Protect samples from the sun. For tests that require refrigeration, use a cooler with ice or refrigerated plates, without freezing the sample. Conservation varies depending on the parameter; Also confirm which measurements need to take place on site. Deliver the vials to the laboratory within the deadline informed for each analysis.
What parameters to ask for localized irrigation
A widely used reference to assess the risk of clogging is the table by Bucks and collaborators (1979), reproduced by Batista and collaborators (2008) for drippers with a nominal flow of up to 12 L/h:
| Parameter | Low risk | Moderate risk | Severe risk |
|---|---|---|---|
| Suspended solids (mg/L) | < 50 | 50 – 100 | > 100 |
| pH | < 7,0 | 7,0 – 8,0 | > 8,0 |
| Dissolved solids (mg/L) | < 500 | 500 – 2.000 | > 2.000 |
| Total iron (mg/L) | < 0,1 | 0,1 – 1,5 | > 1,5 |
| Manganese (mg/L) | < 0,1 | 0,1 – 1,5 | > 1,5 |
| Hydrogen sulfide (mg/L) | < 0,2 | 0,2 – 2,0 | > 2,0 |
| Bacterial population (nº/mL) | < 10.000 | 10.000 – 50.000 | > 50.000 |
This is a historical framework for evaluating clogging potential. It does not constitute a potability standard or complete assessment of the agronomic suitability of the water. Confirm the method and unit of bacterial analysis with the laboratory before comparing results.
Based on this framework, and with some usual complements, the analysis request for localized irrigation usually includes suspended solids and turbidity, pH, electrical conductivity or dissolved solids, iron, manganese, sulfides and a biological evaluation. When there is fertigation, discuss with the laboratory and the designer the inclusion of parameters linked to the formation of precipitates, such as calcium, magnesium and bicarbonates. The final list depends on the source, area history, and system.
Beyond clogging: salinity, infiltration and toxicity
Water also needs to be evaluated in relation to the soil and crop. The FAO distinguishes the risks of salinity, reduced infiltration and toxicity from specific ions. Therefore, discuss with the laboratory the determination of electrical conductivity, sodium, calcium, magnesium, chloride and boron, in addition to calculating the sodium adsorption ratio (RAS).
Infiltration must be interpreted by combining RAS and electrical conductivity, along with soil conditions. For sodium, chloride and boron, the assessment also depends on the sensitivity of the crop and management. A favorable result in the clogging situation does not alone demonstrate that the water is suitable for any soil or crop.
How to read the report without falling into traps
- The risk class is a warning, not a sentence. Clogging often combines physical, chemical and biological factors, Virginia Tech Extension explains. A parameter in the low range does not compensate for another in the severe range, and moderate combinations can also cause problems.
- Iron deserves special attention. In the study of Rural Science, the water had iron between 2.3 and 3.1 mg/L in the catchment and in the evaluated sectors, classified by the authors as "very high" risk (above 1.5 mg/L, the severe Bucks range), although dissolved salts were very low. Clean-looking water may have dissolved iron in it.
- A sample is a photograph. The quality of dams and rivers can vary throughout the year: in the rainy season, floods can carry more sediment and organic matter to surface catchments. Repeating the analysis in the dry and rainy season better shows the variation that the system needs to support.
- The sender matters. The Bucks table is presented for drippers up to 12 L/h; micro sprinklers and other flow rates may have different tolerances. The filtration and treatment decision must consider the report together with the equipment.
Hypothetical example of interpretation
Assumptions (illustrative values, not real property): dam used for drip coffee, with suspended solids report of 70 mg/L, pH 7.4 and total iron of 0.8 mg/L. According to Bucks' table, the three parameters are in the moderate risk range. This alone does not define the solution. The project needs to discuss the degree of filtration, assess whether there is a need for iron treatment and how to retain any precipitates before the emitters and establish a cleaning routine. It is also necessary to know the source variation and other agronomic parameters; These three results do not demonstrate the suitability of water for coffee.
FAQ
How many times a year should I analyze irrigation water? There is no single number. In surface sources, analyzing the dry and rainy seasons helps to understand the variation. Repeat when changing the source, when a blockage with no clear cause appears, or when the appearance of the water changes.
Can I use a bottle of soda or mineral water? The safest thing is to use the bottle provided or indicated by the laboratory, which knows the requirements of each analysis.
Does water analysis replace soil analysis? No. They complement each other. Water analysis assesses risks to the system, soil and crop, including clogging, salinity, infiltration and toxicity by specific ions. Soil analysis helps to interpret these risks in the conditions of the area and guide fertilization and management.
Well water does not need filtering? Not necessarily. Groundwater may have dissolved iron, manganese or sulfides which, in contact with the air in the system, can oxidize and form deposits or encourage bacteria. Only the report, combined with the type of issuer, allows the treatment to be defined.
Conclusion
The report of an irrigation water analysis is only reliable if the sample is representative. Collecting at the right point, using the bottle and procedure indicated for each test, removing stagnant water according to the well purging criteria, identifying and preserving the sample and respecting the laboratory deadline make a difference in the diagnosis. Then, the reading must consider the emitter, filtration, time of year, soil and crop, without treating any isolated value as a recipe.
If you are going to implement or review a drip or microsprinkler and you already have (or intend to do) a water analysis, the Perin Irrigação team can help interpret it in the context of the project. Send the municipality, crop, approximate area and water source via WhatsApp (14) 99824-5219 or by email contato@perinirrigacao.com.br.
Sources consulted
Research carried out on 10/23/2026.
- PRADO, R. B.; TAVARES, S. R. L.; BEZERRA, F. B.; RIOS, L. C.; ESCALEIRA, V. Technical manual for collection, packaging, preservation and laboratory analysis of water samples for agricultural and environmental purposes. Rio de Janeiro: Embrapa Solos, 2004 (Documents, 65).
- BATISTA, Rafael O.; SOARES, A. A.; SOUZA, J. A. R.; BATISTA, Raquel O. Empirical models of localized irrigation with treated sewage. Engineering in Agriculture, Viçosa, v. 16, no. 3, p. 369-377, 2008 (replicates the criteria of Bucks et al., 1979).
- RIBEIRO, T. A. P.; PATERNIANI, J. E. S. Micro sprinklers clogged due to iron problems in the water. Rural Science, Santa Maria, v. 38, no. 5, p. 1456-1459, 2008.
- FAO. Water quality for agriculture. Irrigation and Drainage Paper 29, revision 1, 1985. Section 1: water quality assessment.
- SHORTRIDGE, J.; BENHAM, B. Filtration, Treatment, and Maintenance Considerations for Micro-Irrigation Systems. Virginia Cooperative Extension, publication 442-757 (BSE-222P).
- UTAH STATE UNIVERSITY EXTENSION. Additional Monitoring Protocols — Water Chemistry Sample Collection.
- RODRIGUES, C. Sampling and Shipping Instructions for Microbial Analysis of Agricultural Water. Alabama Cooperative Extension System/Auburn University, 2022, ANR-2904.
