Water Quality

The quality of irrigation water can influence plant growth, the structure and condition of the soil and the effectiveness of water application through irrigation. For instance, bore water from a shale or quartz-based aquifer can have a low pH, which can lead to nutrient leaching and nutrient deficiencies. Bore water from a dolomite or limestone aquifer can have a high pH, plus high calcium or magnesium content which can clog up irrigation lines and sprinkler heads and reduce the water flow to your crop.

Water quality tests can help to identify any issues and allow the grower to manage their irrigation more effectively. Growers must match their nutrition to their water quality parameters, soil and leaf nutrient testing will provide appropriate recommendations for both water types.

Water sampling & tests

A general physical and chemical analysis of water quality generally requires:

1L of water is sampled in a bottle with no air gap;
Stored <6°C; and
Supplied to a laboratory within 48 hours.

Water quality parameters

Although there is little published research to define the limits to water quality parameters for mango production, a general guide for salt content, pH, alkalinity and hardness of irrigation water is provided below.

Table 3. Primary irrigation water quality parameters (Adapted from WA AGRIC, 2019. Water salinity and plant irrigation).

	Description	Suitable Range
Salinity	Salts in irrigation water are mainly common salt (sodium chloride), calcium and magnesium bicarbonates, chlorides and sulphates. The salinity of water is usually estimated from its electrical conductivity (EC), which can be converted to total dissolved solids (TDS). The EC does not identify the salts present but gives a fairly reliable indication of salinity problems. EC is measured in milliSiemens per metre (mS m-1).	<1000 mgL-1 TDS
pH	The test for pH measures the balance between positive hydrogen ions and negative hydroxyl ions. This test indicates if water is alkaline (pH >7), neutral (7) or acid (<7).	pH 5.5 to 8.5 is suitable for most plants. If pH <6, corrosion of metal pipes and fittings can start. If pH <4, water can contribute to soil acidity. If pH >8.5 or <6, spray mixes can be affected.
Alkalinity	Alkalinity is a measure of the total or hydroxyl ions. It is mainly caused by the presence of bicarbonates and carbonates in the water, and should not be confused with the measurement of pH. It is measured as mg/L CaCO3 equivalent.	<90 mgL-1 – low risk of problems occurring. 90–335 mgL-1 – moderate risk declining soil structure, reduced plant growth from prolonged use, and accumulation of a white scale on plants spray-irrigated in high humidity weather. >335 mgL-1 – high risk of soil problems and reduced plant growth, and a build-up of scale, which blocks metal pipes >500 mgL-1 – can be harmful to human health, but water develops an unpleasant taste well before this level.
Hardness	Hardness means the concentration of all the metallic cations in water. It is a measure of the dissolved calcium and magnesium salts and is expressed as mg/L CaCO3. Over time, hard water can block hot water systems, metal pipes and irrigation fittings, and can reduce soil structure.	Water with less than 100 mgL-1 CaCO3 is generally regarded as suitable for most uses. Suggested hardness limits are: 300 mgL-1: for mixing chemical sprays and dips, and can have an adverse effect on soil structure. >500 mgL-1: limit for most other uses.

Water quality issues

Read more Physical and chemical parameters of irrigation water can impact soil health and structure.

Farm water quality and treatment factsheet from NSW DPI.

pH

Read more The pH level of water can accrue in the soil over time, changing the soil pH, and the nutrients available to the plant.

Read more about pH ranges and the effect on soil on the Queensland Government webpage.

Sodium

The physical structure of soil can be altered by irrigation of water with high sodium content, causing the development of sodic soil. The three main problems caused by sodium-induced dispersion are:

reduced infiltration
reduced hydraulic conductivity
surface crusting

Read more Sodic soils on the WA DPIRD webpage

Boron toxicity

Irrigation water in Carnarvon can contain moderate to high levels of boron (0.2 to 1 mgL-1). Water with a boron concentration over 0.5 mgL-1 is considered marginal for sensitive crops such as avocados, grapes and stone fruit, but no information is available for mangoes. Irrigation water high in boron can result in the accumulation of boron in the trees root zone. A symptom of boron toxicity in mangoes is a wavy burn pattern along the margins of older leaves starting at the leaf tip.

Hard water

Water with high concentrations of calcium salts can calcify over time, blocking irrigation equipment including sprinkler heads, irrigation lines etc. This reduces the water flow through the system.

Read more Farm water quality and treatment factsheet from NSW DPI, includes information on treating hard water.

Particles

The efficacy of irrigation can be altered by water quality through the deterioration of irrigation infrastructure. Water with high concentrations of particles or solids will require filtration to ensure irrigation infrastructure does not block over time.

Salinity

Read more Salinity and the effect on soil on the WA DPIRD webpage