For too long, drinking water hardness has been treated as little more than an aesthetic issue – a matter of taste or scaling in kettles. But the latest evidence tells a different story, and I believe it’s time we update our thinking and our standards.

The Australian Drinking Water Guidelines currently recommend a hardness limit of 200 mg/L. But these limits were developed decades ago, and in reviewing the most recent national and international data, it’s clear they no longer reflect what we now understand about the health and infrastructure impacts of hardness. In fact, many countries still quote standards developed in the 1980s. That’s more than 40 years without meaningful revision.

Recent findings suggest that excessive hardness may contribute to arterial calcification – a concern for public health, particularly as our population ages. It also complicates fluoridation efforts by forming insoluble compounds with fluoride, making it more difficult to maintain consistent fluoride levels in supply. And it causes increased pressure losses in water pipes, translating to real energy costs for utilities – especially where ageing infrastructure is already under strain.

Despite these concerns, the Guidelines devote just a page and a half to the topic of hardness in over 1,200 pages of detailed analysis. The only reference for health effects is from 1977 – and even that suggests benefits, not risks. This oversight is striking given that the same document offers an example of a water system with a hardness range between 15 and 35 mg/L – far below the current recommended maximum. And cities like Hobart, Canberra and Sydney already sit well below the 60 mg/L mark.

So why are we still holding on to a 200 mg/L threshold?

It's time for a rethink. I believe the recommended limit in the Guidelines should be revised down to 60 mg/L. This level is both practical and safe – and aligns with values already in place across much of Australia.

Inaction risks compromising our public health goals and efficiency in water management. The science has moved on. Our standards should too.

Nick Standish is an Emeritus Professor of Engineering and member of the Australian Water Association.

Response to article: “Why it is Time to Take Hard Water Seriously” 

Robert Ford  AWA Member 

The 10 July issue of Source included an opinion piece which questions the current hardness levels specified in the Australian Drinking Water Guidelines (ADWGs). It claimed that “Recent findings suggest that excessive water hardness may contribute to arterial calcification” (Standish, 2025) . While the topic is certainly of public interest, it was my understanding that this issue was well settled some years ago.  

When relevant research is identified, it is important to critically analyse the findings to determine their reliability and strength. This is particularly relevant when contradictory results are in existence. It is also important to understand  the quality of evidence upon which any argument is based (FACS Insights., 2020). 

Contrasting findings
To gain an understanding of the current state of knowledge of the health effects of hard water, I performed a cursory search of three academic databases (Medline, Scopus and Web of Science) to locate any relevant systematic reviews, or meta-analyses on the association between water hardness and arterial calcification, atherosclerosis or myocardial infarctions (heart attack). Three systematic reviews were located, covering a total of 32 individual peer reviewed studies. A summary of these results follow.  

Bykowska-Derda, et al (2023) undertook a systematic review of the relationship between mortality from cardiovascular disease (CVD) and total drinking water hardness.  Of the 25 studies reviewed, over a quarter reported a nil or non-significant relationship between water hardness and CVD.  No studies indicated any negative health impact of hard water on CVD. Three other studies provided sufficient data for a meta-analysis to be performed. Results of this analysis indicated that drinking hard water reduced mortality from CVD by 40%. However, the authors did advise that their conclusions should be treated with caution because of methodological shortcomings in the original data sets.  

A systematic review by Lei Jiang et al (2016) explored Magnesium levels in drinking water and its associations with coronary heart disease mortality risk. Nine articles were included, covering 77,821 coronary heart disease (CHD) cases. Four of the studies reported that higher levels of Magnesium in drinking water reduced the CHD mortality risk, whilst four other studies reported an increased, but non-significant, risk.

Finally, Glanfredi et al (2017) investigated associations between CVD and hard drinking waters. A total of seven studies were reviewed. These examined the relative effects of Calcium (17,000 subjects) and Magnesium (19,000 subjects) on CVD. Results indicated an inverse relationship between cardiovascular diseases for both minerals, suggesting a potentially beneficial health effects of hard water.  

Confounding variables
A major risk to the validity of epidemiological studies is failure to control confounders. Given the complexity of cardiovascular health and the many variables that can influence arterial calcification, any analysis needs to address the potential role of confounding factors.  Determinants of vascular calcification have been extensively investigated in medical literature and can include age, sex, genetic factors, levels of physical activity, socioeconomic status, smoking and diet (Schmidt–Truckäss, 2024).

Conclusion
Discussions on drinking water quality are important, and opinion pieces can be a useful way to raise emerging or minority views. At the same time, it is important for readers to review the supporting evidence and evaluate the strength of the claims. In the case of hard water and cardiovascular health, the body of recent research does not present a clear-cut case for harm and in some instances suggests possible benefits. Continuing to assess and debate these topics using transparent, well-sourced evidence will help ensure public understanding and policy decisions remain well-grounded. 

References
BYKOWSKA-DERDA, A., SPYCHALA, M., CZLAPKA-MATYASIK, M., SOJKA, M., BYKOWSKI, J. & PTAK, M. 2023. The Relationship between Mortality from Cardiovascular Diseases and Total Drinking Water Hardness: Systematic Review with Meta-Analysis. Foods (Basel, Switzerland), 12. 

FACS INSIGHTS., F. 2020. What is an evidence hierarchy? [Online]. NSW Government. Available: https://dcj.nsw.gov.au/documents/about-us/facsiar/evidence-hub/evidence-how-to-guides/what-is-an-evidence-hierarchy.pdf [Accessed July 2025]. 

GIANFREDI, V., BRAGAZZI, N. L., NUCCI, D., VILLARINI, M. & MORETTI, M. 2017. Cardiovascular diseases and hard drinking waters: implications from a systematic review with meta-analysis of case-control studies. Journal of water and health, 15, 31-40. 

JIANG, L., HE, P., CHEN, J., LIU, Y., LIU, D., QIN, G. & TAN, N. 2016. Magnesium Levels in Drinking Water and Coronary Heart Disease Mortality Risk: A Meta-Analysis. Nutrients, 8. 

SCHMIDT - TRUCKSÄSS, A. LICHTENSTEIN, A. VON KÄNEL, R. (2024).  Lifestyle factors as determinates of atherosclerotic cardiovascular health. Atherosclerosis 395, 117577 

STANDISH, N. 2025. Rethinking hardness in drinking water. SOURCE July 10th 2025. Australian Water Association.