Gardeners using scheme water for reticulation can usually be assured of good quality water which has low salt levels. Many gardens, however, are equipped with wells or bores that use groundwater supplies. These water sources can contain salt levels that are harmful to plant growth and the physical conditions of soil.
Water quality can also affect fertility needs, reticulation system performance and longevity, and how the water can be applied. These factors make knowledge of water quality critical to understanding the management of a healthy garden.
Home gardeners should have their bore water tested before applying it to the garden. A number of analytical laboratories will analyse water including Chemistry Centre WA or consult the internet or Yellow Pages directory for other testing centres under ‘Analysis’. Fees are charged for water testing and this web article will assist in the interpretation of test results.
Gardeners should take into account the fact that bore water quality changes with the seasons.
There are a number of factors in reticulated water that can be tested. For Western Australian home gardeners, it is usually enough to test total soluble salts, total solids, pH, iron content and, in arid regions, the boron content.
Total soluble salts are usually measured by the electrical conductivity of the water and are quoted as millisiemens per metre (mS/m). Multiply the conductivity (in mS/m) by 5.5 to convert approximately to milligrams per litre (mg/L) or parts per million (ppm).
The suitability of water for reticulation and home gardens is influenced not only by the total soluble salts and their composition, but also by the type of soil and its drainage, the climate and the rainfall. Salts accumulating in the soil from the reticulated water can cause a salt problem.
Using saline water
Seedlings are more sensitive to salt than mature plants. In salty situations it may help to grow seedlings in poting mix in containers that break down when the plants are placed in their permanent positions. Saline water can be used more successfully on a well-drained light soil than on a poorly-drained heavy soil. Plants have more tolerance to salty water in districts where high seasonal rainfall leaches the salts accumulated in the soil.
Trickle systems can reduce the effects of salinity by maintaining a continuously moist soil around the plant roots and providing steady leaching of salt to the edge of the wetted zone. If saline water is used for sprinkler systems, it is important to reduce evaporation.
Improve soil structure by applying gypsum to heavy soils that have been shown to become more friable with gypsum and add big quantities of organic matter to all soils.
Water at night, early in the morning, or late evening when the air is more humid. Watering in the heat of the day or during high winds concentrates the salts due to the high evaporation. Do not use sprinklers that produce fine droplets and if possible avoid intermittent sprinklers, especially slow revolution sprinklers, that allow drying periods and cause salt to build up on the leaves.
Generally, 635mS/m (or 3500mg/L) of total salts is regarded as the maximum safe level for watering of any plants. With this salt content drainage must be excellent and each watering should apply enough water to leach accumulated salts below the roots of plants. Keep the water off the leaves to avoid burning. Where reticulation is used infrequently or only for short periods during the year, more saline water may be used. When watering with saline water closely observe the growth and condition of plants or herbage. Saline water can cause considerable yield loss before symptoms of leaf burn become obvious.
Testing water for total soluble salts
Samples should be at least 500mL in a clear glass or plastic bottle, previously well rinsed with the water to be sampled. Use a clean, screw cap, cork or stopper to seal the bottle, and mark the bottle itself with the sender’s name and address, and the date of sampling.
Total solids in reticulation water
High levels of total solids such as clay or silt in water can cause problems including blocked nozzles and filters, excessive wear of pumps and nozzles, and adsorption of chemical molecules. This tie-up of chemicals, particularly by suspended clay particles, will reduce the effectiveness of some pesticides.
pH and alkalinity
Excessively acid or alkaline water may affect the uptake of nutrients by plants. It also may reduce the performance of some pesticides and damage the reticulation system. The acidity or basicity of reticulation water is expressed as pH (< 7.0 acidic; > 7.0 basic). The normal pH range for reticulation water is from 6.5 to 8.4.
Many underground waters contain iron. Water containing iron in solution may be clear and colourless when first drawn, but becomes cloudy and eventually deposits reddish-brown hydrated iron oxide after standing in contact with the air. Iron in water stains clothes, buildings and pathways brown when used in sprinklers on nearby gardens. This can be a problem with sprinkler usage on fruit trees and nursery plants. Iron deposits may block trickle systems. There is no simple method of removing iron, so garden sprinklers should be sited to prevent spraying buildings and places where the stain might be conspicuous.
In arid areas excess boron may be a problem in the garden. If the water supply is considered suitable for the garden, yet beans, radish and citrus suffer, a check for boron is advisable.
Plant tolerance to saline water
The tolerance of plants to salt water varies. In the table below, plants are arranged in approximate order to salt tolerance in each group, with the least tolerant listed first. The difference between two or three plants near one another in each list is small.
These plant and water groups are only a general guide, as soil texture and drainage could be overriding factors. Plants listed as suitable for salty waters will grow better with less salty water.
|Water group A conductivity 0–90 mS/m: Highly salt sensitive plants|
Precautions for reticulation use:
Fruit: persimmon, passionfruit, strawberry, raspberry, avocado, loquat, almond, stone fruit, citrus fruit, apples, pears.
Vegetables: green beans, parsnips, celery, radish, squash, peas, onion, carrot.
Ornamentals: primula, gardenia, star jasmine, begonia, rose, azalea, camellia, ivy, magnolia, fuschia.
Water group B conductivity 90–270 mS/m: Mildly salt sensitive plants
Precautions for reticulation use:
Fruit: mulberry, grape.
Vegetables: cucumber, capsicum, lettuce, sweet corn, rockmelon, potatoes, cauliflower, cabbage, watermelon, broccoli, pumpkin, tomato.
Ornamentals: hibiscus, geranium, gladiolus, bauhinia, zinnia, aster, poinsetta, lantana, Thuja orientalis, hop bush (Dodenea attenuata), banana (Musa spp), emu bush (Podocarpus), Juniperus chinensis, bottle brush (Callistemon viminalis).
Water group C conductivity 270–635 mS/m: Slightly salt sensitive plants
Precautions for reticulation use:
Fruit: olive, fig, pomegranate.
Vegetables: spinach, asparagus, kale, garden beets.
Ornamentals: stock, chrsyanthenmum, carnation, oleander, rosemary, bougainvillea, vinca, copromosa, Ficus spp., false acacia (Robinia pseudoacacia), Queensland pyramid tree (Lagunaria patersonii), NZ Christmas bush (Metrosideros tomentosa), bangalay (Eucalyptus botryoides), river red gum (E. camaldulensis), Rottnest tea tree (Melaleuca cupressiformis), Rottnest cyprus (Callitris robusta), Acacia longifolia, buffalo grass, kikuyu grass, portulaca, Mesembryanthemum, boobialla (Myoporum acuminatum), red mallee (E. oleosa), swamp yate (E. occidentalis), York gum (E. loxophleba), swamp mallet (E. spatulata), couch grass, bamboo, Kondinin blackbutt (E. kondininensis), swamp cypress (Actinostrobus pyramidalis).
Water group D conductivity 635–2365 mS/m: Salt tolerant plants
Precautions for reticulation:
Fruit: date palm.
Ornamentals: canary palm (Phoenix canariensis), salt river gum (E. sargentii), saltwater couch, salt lake honey myrtle (Melaleuca thyoides), salt sheoaks (Allocasuarina cristata and A. glauca), tamarisk, saltbush (Atriplex nummularia).
Yield and growth of all plants is reduced with saltier water.