Water testing

Irrigation Water Testing

Testing to determine whether a source of water will be suitable for irrigation water.

Taking a Sample | Guides and Supporting Information | Contact us Today

About this Testing

Irrigation water is becoming increasingly important in parts of New Zealand, particularly on the east coast of the South Island where rainfall can be scarce. Because irrigation water often has significant levels of dissolved salts, it can have a detrimental effect not only on the irrigated soil, but also on the pumping equipment used. It is therefore important to test the water in order that any issues may be anticipated and the productivity of irrigated land and associated water resources maintained.
Guidelines for Irrigation water quality can be found in the ANZECC guidelines. These guidelines cover a wide variety of analytes, therefore we have selected the most appropriate for the irrigation water testing.

Testing irrigation water is covered by our Irrigation Water profile:

Test	ANZECC Trigger Value	Comment
pH	6 - 8.5	pH < 5 indicates a high corrosion potential for irrigation watering systems pH > 8.5 indicates an increased fouling potential for irrigation watering systems (groundwater)
Hardness	60 - 350mg/L CaCO3	< 60mg/L has an increased corrosion potential > 350 indicates an increased fouling potential
Langelier Saturation Index (LSI)	-0.5 - 0.5	< -0.5 indicates an increased corrosion potential > 0.5 increased fouling potential
Faecal Coliforms	<10 per 100mL <100 per 100mL <1000 per 100mL	Raw Food crops in direct contact with irrigation water Pasture and fodder for dairy animals (without withholding period) Pasture and fodder for dairy animals (with withholding period of 5 days). Also for Raw human food crops not in direct contact with water.
Electrical Conductivity (EC)	N/A	EC is used in conjunction with the SAR (see below) in order to determine whether soil sturctural problems are likely or not.
Sodium Adsorption Ratio (SAR)	<2	SAR values of 2 - 8 are likely to cause leaf tip burn and leaf scorch on extremely sensitive crops such as avocado, nuts and citrus.
Chloride	<175 mg/L	Water containing more than 175mg/L of chloride is likely to cause foliar injury to sensitive crops (e.g. citrus, plum and grape). High levels of chloride (>750 mg/L) can release cadmium from the soil.
Sodium	<115 mg/L	Water containing more than 115mg/L of sodium is likely to cause foliar injury to sensitive crops (e.g. citrus, plum and grape). Excessive levels of sodium in the soil can destroy its structure leading to decreased water permeability.
Nitrogen	<5 mg/L	Excess quantities of N can lead to leaching of N into groundwater and surface water, overstimulation of plant growth (decreasing yields) and stimulation of algal growth in surface water.
Phosphorus	<0.05 mg/L	P is often the nutrient that stimulates rapid growth of many microorganisms (i.e. algal blooms). It can also cause bioclogging of irrigation equipment.
Copper	<0.2 mg/L
Manganese	<0.2 mg/L
Arsenic	<0.1 mg/L	Can be present in groundwater from Geothermal sources.
Boron	<0.5 mg/L	Can be present in groundwater from Geothermal sources.

Taking a Sample

When taking the sample, it is very important to follow the instructions provided, especially for the Ecoli test. This requires a sterile container (square plastic 400mL) and the tap needs to be sterilised to make sure that no contamination occurs. Also note that we need the samples back with 24 hours and less than 10°C, otherwise the results will not be valid. For clients who are not within easy driving distance from Hamilton or Christchurch, we suggest taking your sample in the early afternoon and sending it overnight to the laboratory.

Sampling equipment:

Request a Routine Water Kit from the Laboratory. It contains 3 sample containers which are all required for one test, i.e. they should all be filled from the same sampling point, not from 3 different points.

Unsure about the correct container to use to submit a sample? Consult our container guide

Guides and Supporting Information

Technical note Microbes in private water supplies