Choosing a detergent to match your water hardness
Water is often described as soft, moderately hard and hard. Water hardness affects your laundry and how much detergent you need to use.
Water is often described as soft, moderately hard and hard. This is based on the amount of dissolved minerals in water.
The harder the water is, the more minerals there are to compete with the surfactants in detergent. This means you need to add more detergent in harder water or use water-softening agents.
Table of contents
Adapting laundry to your water hardness
Your water hardness not only determines how much detergent, but also what type of detergent your laundry needs.
Powder detergents have a water-softener base, usually sodium carbonate. This water softener binds to minerals in the water, allowing the surfactant in the detergent to work effectively. For this reason powder detergent is usually preferred in hard water areas.
Liquid detergents generally don’t contain water softeners. Since soft water doesn’t contain many minerals, liquid detergents are usually a better option in soft water areas.
| Classification | mg/L & ppm | Grains/Gallon | Detergent considerations |
|---|---|---|---|
| Soft | 0–17 | <1.0 | Water is soft and will lather very well. Likelihood of oversudding with powder detergents. Consider using a liquid detergent |
| Slightly hard | 17.1–60 | 1-3.5 | We consider this as ‘soft water’ but without the concerns of oversudding. Can use most detergents. |
| Moderately hard | 61–120 | 3.5-7.0 | Most detergents will work well. Consider using a powder detergent. Add a laundry booster for poorer quality detergents. |
| Hard | 121–180 | 7.0-10.5 | Increase standard detergent dose by 50% or add laundry booster or water softeners routinely. |
| Very hard | ≥181 | >10.5 | Double standard detergent dose or add laundry booster or water softeners routinely. |
Reducing laundry costs with hard water
Increasing the amount of detergent you use can become costly. If you have hard water, there are several ways to reduce your laundry costs and still have clean laundry:
- Adding a powdered laundry booster.
- Adding water-softening agents (for example, Lectric Washing Soda).
- Pairing a high-performing detergent with a budget detergent that contains a high percentage of water-softening agents.
- This can be more affordable than buying a standalone water softening agent or laundry booster.
- Australian/ NZ: Coles Simply Lemon Laundry Powder and Woolworths Clean Laundry Powder Lemon Fresh.
- North America: Arm & Hammer plus OxiClean.
Stain removal for different water hardness
If you have extremely soft water and stubborn stains, using a powder laundry booster is likely to cause excess suds. Instead of using a laundry booster, consider using chlorine bleach for stain removal or adjusting the other cleaning factors.
Chlorine bleach works for all water hardness and machine types. It is the most effective and efficient way to remove biological stains such as poo and food.
| Product | In-wash | Cost | Soft water | Hard water | Sustainable1 |
| Bar soap |
Unsuitable option |
Not expensive |
Suitable option |
Suitable option |
Suitable option |
| Stain removal spray |
Unsuitable option |
Expensive |
Suitable option |
Suitable option |
Unsuitable option |
| Laundry booster (oxygen bleach) |
Suitable option |
Cost varies |
varies2 |
Suitable option |
Unsuitable option |
| Chlorine bleach |
Suitable option |
Not expensive |
Suitable option |
Suitable option |
Suitable option |
1. Evaluated based on packaging (use-to-plastic ratio)
2. Using laundry booster in soft water may cause excess suds
Wool and silk require products that have a neutral pH level and are free of proteolytic enzymes (proteases). Use an enzyme-free liquid laundry detergent, and spot treat with bar soap or stain remover gel (liquid Vanish). Avoid using powder detergent, powder laundry boosters or chlorine bleach on these items as the pH is too high.
Finding your water hardness
If you live in a hard water area, you probably know that you have hard water. Detergents, soap and shampoo all lather up with greater difficulty in hard water. Hard water forms deposits that clog plumbing and build up around taps. It usually looks like off-white solids on the inside surfaces of pipes and heat exchanges.
If you are unsure of your water hardness, there are several ways to find out. If you are on mains water contact your water provider or check on your council website. You can also search for your location and water hardness using Google or your preferred search engine.
If you have a water bore the most accurate way to determine your water hardness is to test using a water hardness test strip. These are available from pool shops and hardware stores.
Rainwater and distilled water are soft.
Water hardness around the world
Australian water hardness
Water hardness in major Australian cities ranges from very soft (Hobart, Melbourne, Darwin), to soft (Canberra, Sydney) to moderately hard (Brisbane, Adelaide, Perth).
New Zealand water hardness
Most of New Zealand has soft to very soft water.
UK water hardness
Water hardness varies a lot by region in the UK. Many regions have very hard water (≥200ppm). Regions with very soft water include parts of Wales and Scotland.
North American water hardness
Water hardness in North America is typically hard to very hard.
Understanding water hardness: minerals and measurement
Water hardness is usually expressed as the amount of calcium carbonate (CaCO3/L) in milligrams per litre or parts per million (ppm).
The most important minerals in hard water are calcium ions (calcium sulphate and calcium chloride) and magnesium ions (magnesium sulphate and magnesium chloride). Other minerals (for example, dissolved bicarbonates) are less important because they dissolve in hotter water.
The mixture of minerals dissolved in the water, together with the water’s pH and temperature, determine the behaviour of the hardness; a single-number scale does not adequately describe hardness.
References and further reading
- International Products Corporation, An Easy Guide to Understanding How Surfactants Work <https://www.ipcol.com/blog/an-easy-guide-to-understanding-surfactants/>.
- Wikipedia, Hard water <https://en.wikipedia.org/wiki/Hard_water>.
- Wikipedia, Hard water - Regional information - Australia (April 23, 2020) <https://en.wikipedia.org/wiki/Hard_water#In_Australia>.
- USGS - U.S. Geological Survey Office of Water Quality, USGS Water-Quality Information: Water Hardness (April 23, 2020) <https://www.usgs.gov/special-topic/water-science-school/science/water-properties-information-topic>.
- knowyourh2o, Water Hardness Levels - | Hard Water Hardness Calcium Magnesium Water Corrosion Mineral Scale (December 14, 2023) <https://www.knowyourh2o.com/indoor-6/hardness>.
- USGS (United States Geological Survey), Hardness of Water (July 5, 2025) <https://www.usgs.gov/special-topics/water-science-school/science/hardness-water>.
- Foundation for Advancement in Conservation, Soaps, Surfactants, and Detergents (July 14, 2025) <https://cool.culturalheritage.org/conservation-science-tutorials/tutorials/soaps.html>.
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