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Laboratory analysis for irrigation water

Sampling and monitoring of irrigation water

Before supplying recycled water for irrigation purpose, there should be performed an analysis of the quality of this water, interpreting results, search for solutions (i.e. good management practice, use of water treatment solutions and technology as provided by Lenntech) and monitoring frequently.

For example, water with low quality and big concentration of salt may require a reverse osmosis treatment system. Water with only minor quality problems may only require slight changes in supplemental fertility.

The procedure to take samples will affect the precision and reliability of the water quality data and determine its interpretation. it is important to monitor quality standards on a frequent basis to avoid potential problems.

Some general considerations to take into account when making lab test of irrigation water are listed below:

- Usually 1L of sample is sufficient

- All samples should be labelled to indicate date, location, time and other pertinent data.

- Take seasonal samples for representative data due to variation of water quality by climate conditions

- Take samples before and after the treatment plant for recycled water and other representative samples when appropriate such as after the storage tank, etc.

Recommendations for samples preparation & conservation

The following table compile the recommendations for samples preparation & conservation

Parameter Type of bottle1 Addition of chemicals Conservation Comments
Anions and cations (Chloride, sulphate, etc.), all forms of nitrogen and phosphorus, as well as general physicochemical parameters (PH, SS, conductivity, etc.) 1 L plastic, with or without air No additive Dark, 4°C Temperature and dissolved oxygen should be measure on site
COD 100 mL, plastic, no air Sulphuric acid Dark, 4°C No additive is needed if the samples are analyzed within 48h
BOD 500 mL, plastic, no air No additive Dark, 4°C
Trace elements 250mL, plastic, with or without air Nitric acid Dark, 4°C A special bottle and additive is needed for the analysis of mercury (Hg)
Trace organics and pesticides 1L, dark glass bottle, no air No additive Dark, 4°C
Microbiological parameters (total and faecal coliforms, heminths, viruses, etc.) 1-5L, sterile plastic bottle, with air No additive Dark, 4°C Additive should be added only to disinfected effluent (sodium thiosulfate in presence of residual chlorine)

Source of information: Valentina Lazarova Akiçca Bahri; Water Reuse for irrigation: agriculture, landscapes, and turf grass; CRC Press.

1. Plastic bottles are preferred because glass bottles may introduce boron to the samples.

The following table compile the recommendations for samples preparation & conservation:

Monitored parameters Raw wastewater & recycled water Receiving soils Groundwater
Shallow aquifers Deep aquifers
Weekly to monthly - Bi-annual Annual
Turbidity On-line for unrestricted irrigation - - -
Chlorine residual On-line for unrestricted irrigation - - -
Monthly - - -
Water level
- - Bi-annual -
PH Monthly Annual Bi-annual Annual
Suspended Solids Monthly - - -
Total dissolved solids Monthly - Bi-annual Annual
Conductivity (ECi)
Monthly Bi-annual (ECe) Bi-annual Annual
Monthly - - -
Monthly - Bi-annual Annual
Monthly - Bi-annual Annual
Monthly Annual (exchangeable NO3) Bi-annual Annual
Total Nitrogen
Monthly Bi-annual Bi-annual Annual
Total phosphorus Monthly Bi-annual (extractable P) Bi-annual Annual
Phosphates (soluble) Monthly Bi-annual Bi-annual Annual
Major solutes (Na, Ca, Mg, K, Cl, SO4, HCO3, CO3) Quarterly Bi-annual Bi-annual Bi-annual
Exchangeable cations (Na, Ca, Mg, K, Al) Annual - -
Trace elements - - -

Source of information: Valentina Lazarova Akiçca Bahri; Water Reuse for irrigation: agriculture, landscapes, and turf grass; CRC Press.

Related pages:

Bicarbonate hazard of irrigation water

Irrigation water quality

Nutrients in irrigation water

Salinity hazard irrigation

SAR hazard of irrigation water

Toxic ions hazard of irrigation water

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