Salinity and drinking water
The River Murray accounts for 40% of Adelaide’s water supply. In a drought year this can increase to 90%.
Historical data shows that the salinity of Murray water is dependent on the flow, which could increase dramatically during a drought.
Will this water still be safe to drink? The answer is yes – for the general population. The main issue will be the saltier taste that water at some locations may develop.
The total amount of salt in the water can affect the taste of water. Taste is extremely personal; some people prefer rainwater, others prefer water straight from the tap or a bore.
How salinity is measured
Salinity relates to the amount of salt in the water, where the salt can be in many different forms (salt used in food is sodium chloride). Typically Australian waters can contain two or more of the following salts:
There are two main methods of defining the concentration of salt in water:
- Total Dissolved Solids (TDS) - measured by evaporating water to dryness and weighing the solid residue
- Electrical Conductivity (EC) - measured by passing an electric current through the water and measuring how readily the current it flows
TDS are recorded in milligrams per litre (mg/L) or parts per million (ppm). The standard EC unit is microSiemens per cm (µS/cm). It is often referred to simply as an 'EC Unit'.
The TDS analysis is generally considered a more accurate measure of salinity. However, determining EC is much simpler and quicker, using a portable handheld instrument. EC is often used to give an estimate of TDS as a result, using the following approximation.
TDS (mg/L) ≈Salinity (EC) x 0.55
The conversion factor “0.55” is used for River Murray water but this value ranges from 0.5 to 0.7 depending on the water source.
Current TDS in SA water
- rainwater usually <100 mg/L
- metropolitan tap supplies 150-400 mg/L
- bores water can exceed 1000 mg/L
TDS guideline levels
Guideline levels for TDS in drinking water is based on quality (taste), not safety (health risk).
TDS guidelines vary because they are based on panels of tasters describing water which is very subjective and dependant on personal preference and to what a person is accustomed.
Australian Drinking Water Guidelines
Australian Drinking Water Guidelines stipulate:
- “based on taste, TDS in drinking water should not exceed 500 mg/L” although “water with a TDS content of up to 1000 mg/L is acceptable to many”
- water will become increasingly undrinkable in the 1000 to 2000 mg/L range.
Based on taste, the following categories are provided to rate drinking water according to TDS concentrations:
- less than 600 mg/L is regarded as good quality drinking water.
- 600 to 900 mg/L is regarded as fair quality.
- 900 to 1200 mg/L is regarded as poor quality.
- greater than 1200 mg/L is regarded as unacceptable.
World Health Organization
World Health Organization comments on guideline TDS levels are:
- “The palatability of water with a total dissolved solids (TDS) level of less than about 600 mg/L is generally considered to be good; drinking-water becomes significantly and increasingly unpalatable at TDS levels greater than about 1000 mg/L.”
- No health-based limit since TDS is “not of health concern at levels found in drinking-water”.
Health effects of elevated TDS in drinking water
A substantial increase in TDS in the Murray could result in SA drinking water developing a slightly saltier taste but should not pose a significant health risk to the general population.
There could be impacts for those who need to limit their daily salt intake (for example, severely hypertensive, diabetic and renal dialysis patients) and in these cases advice should be sought from a doctor.