It all began with a salt stain.

One afternoon in a kitchen in Cholula, a picturesque town in Puebla, Mexico, a few drops of tap water dried on the sink, leaving behind a chalky white residue. This everyday scene—familiar to anyone living with hard water—sparked the idea that eventually grew into our research. What at first seemed like a simple nuisance revealed a deeper question: what does it really mean to live using hard water, and how can materials science help with it?

Functional polymeric materials for hard water treatment a comprehensive review.

For one of us, the issue was more than aesthetic. Prolonged use of hard water—rich in calcium and magnesium ions—had triggered episodes of eczema, serving as a personal reminder of how water quality can subtly impact health. That experience inspired us to look closer, and soon we realized that the problem extended far beyond a single kitchen or household.

A common problem with global reach

The hard water situation of Cholula is far from unique. As we delved into literature, we were surprised to discover just how widespread hard water is globally. Most cities around the world rely on hard water supplies.

In the United States, more than 85% of households live with hard water. Across Mexico, groundwater hardness is the norm. In Europe, cities such as London and Oxford often exceed 200 ppm CaCO₃, whereas parts of Africa, Asia, and Australia exhibit significant regional variations, depending on their geology and rainfall.

Globally, the numbers are staggering. Hard water affects household appliances, shortens the lifespan of heaters and pipes, increases soap consumption, and contributes to environmental issues such as scaling and energy inefficiency. More importantly, it can impact health, ranging from skin irritation and hair damage to more complex concerns. Research suggests a relationship between water hardness and chronic disease: moderate levels of calcium and magnesium in drinking water may have protective effects against cardiovascular disease and even reduce the risk of some cancers. However, very hard water has increased risks of bladder cancer, malignant melanoma, hematological malignancies, non-Hodgkin lymphoma, and higher rates of breast and prostate cancer compared to soft water.

Understanding this changed the way we thought about that kitchen sink. What appeared to be a local inconvenience was, in fact, part of a global challenge.

Searching for better solutions

Traditional treatments include ion exchange, chemical precipitation, reverse osmosis, and electrocoagulation. They work, but often at a price: high operational costs, fouling, significant energy demands, and chemical waste. Furthermore, such systems are out of reach for many households.

So, that’s when we turned our attention to whether polymers can help with.

Polymers are fascinating due to their versatility in shaping, mechanical properties, and thermal properties, and chemical tunability. Their chemistry can be tailored to interact with specific ions, surfaces can be modified for enhanced selectivity, and their structures—such as hydrogels, membranes, and composites—can be designed for regeneration and reuse. This flexibility opens possibilities that conventional technologies struggle to match.

In our work titled, Functional Polymeric Materials for Hard Water Treatment: A Comprehensive Review, we examined the state of the art:

• Hydrogels, with their remarkable swelling and ion capture capacity, can remove Ca²⁺ and Mg²⁺ with high efficiency.
• Polyelectrolyte systems, like PAA/PVA, calcium chelate, can be processed into membranes or fibrous mats.
• Dextrin-based nanosponges, porous and selective, offer good regeneration cycles.
• Bio-based composites, combining natural polymers with synthetic ones, balance sustainability with performance.

Two sides of the polymer story

Of course, no solution is perfect. Polymers offer several clear advantages, including tunability, selectivity, potential cost-effectiveness, and, in some cases, biodegradability. They can be engineered to be reusable, reducing waste. Some systems already demonstrate over 90% removal of hardness ions under laboratory conditions.

But they also face challenges. Many remain at the proof-of-concept stage, tested with simplified water samples rather than real-world supplies. Some rely on petroleum-derived monomers or energy-intensive processes, raising sustainability concerns. Even biodegradable polymers may have mechanical limitations or degrade slowly under natural conditions. And scalability remains a key barrier—what works in the lab may not yet be viable for households or municipal plants.

In short, polymers hold great promise, but the journey from lab bench to real-world application is still unfolding.

Beyond chemistry: equity and impact

What struck us most while writing this review was not just the science, but the human dimension. Hard water disproportionately affects marginalized communities, where access to expensive technologies like reverse osmosis is limited. In such contexts, this search for polymer-based solutions is more than a technical challenge—it is also a question of equity and sustainability. Designing affordable, regenerable, and environmentally compatible polymer systems, they could transform daily life for millions of people.

From stains to solutions

For us, this journey began with a stubborn salt mark in a Cholula kitchen and the personal struggles that many share, such as skin irritation, scaling pipes, and damaged appliances. It has since expanded from a global perspective, recognizing that the same challenge unites households worldwide.

Our review seeks not only to summarize the progress in functional polymers for hard water treatment, but also to invite further collaboration and innovation. The problem is widespread, but so is the potential for science to address it.

From a single kitchen sink to a worldwide challenge, polymers may one day transform hard water treatment—making it more equitable and sustainable.

Functional polymeric materials for hard water treatment a comprehensive review.