If your existing water source is not suitable for gardening and it is not possible to successfully treat its problems, you will need to find an alternative source. The choice will usually depend on availability and cost.
Common water sources
• Scheme water: Public water supplies are unlikely to be contaminated with industrial pollutants. They are also sterilized and treated to remove color, turbidity, iron and excess CO2. Some suppliers may even treat for problems such as excessive hardness (causes dripper blockages) and low alkalinity (causes corrosion). However, EC (salinity) may be an untreated problem. Suppliers are usually willing to provide a copy of the water’s typical analysis free of charge.
• Rainwater: Rainwater is invariably of low EC and a preferred source if available. To maximize purity, ensure that the run-off area (e.g. roof, gutters) is cleaned prior to the ‘wet’ season, and place a screen on the inlet to the storage reservoir (Fig 6.9). Note also that storage conditions and reservoir design are critical considerations – see section below on “Long term storage of water”.
• Reverse osmosis (RO) water: This requires a high initial capital outlay along with ongoing maintenance expenses. However, it may be the only option if good quality water is not otherwise available (Fig 6.10). For waters that are hard, alkaline, contain iron, color or turbidity, pretreatment is required to avoid damaging the expensive membranes.
• Bore / well or ground water: Although bore (well) waters are usually sterile when fresh, they can have high EC; contain high levels of CO2; hardness; alkalinity; color; turbidity and iron. Other ‘undesirables’ can also be present if the bore is located close to septic tanks, rubbish dumps and industry – including leaky underground petrol station tanks and areas of intensive horticulture.
• Surface water (e.g. rivers, streams, lakes, dams, soaks): These sources are least likely to produce iron and CO2 problems. However, bacteriological quality, turbidity and slimes are key concerns. High turbidity (cloudiness) usually correlates with poor bacteriological quality and potential problems with root borne diseases. Over the warm or dry months there is often an increase in TDS (salinity) because high evaporation rates will concentrate the salts. Surface waters should be dosed prior to use with a suitable disinfectant – see section below on “long term storage of water”.
Long term storage of water
Water, regardless of its source, deteriorates when stored. To minimize this problem, the reservoir should be:
- Covered with an opaque lid to prevent the ingress of dirt, light (causes algae and slimes) and airborne bacteria.
- Located in a cool, dark place. In hot climates, consider burying reservoirs underground.
- Treat the water weekly using a disinfectant – disregard this for waters that are due to undergo reverse osmosis treatment.
© Andrew M Taylor (FloraMax – Chemist)
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