Water Hardness: The Metric for Calcium
Calcium does not have a dedicated health standard because hard water, which contains high levels of dissolved calcium and magnesium, is not a health risk. It is important to distinguish between hard water and water that contains harmful contaminants like arsenic or lead, which are regulated by health standards. Water hardness is measured in milligrams per liter (mg/L), often expressed as calcium carbonate ($CaCO_3$). This is the basis on which water is categorized from soft to very hard. As rainwater filters through rock and soil, it dissolves these naturally occurring minerals, carrying them into aquifers and, subsequently, our water supply.
Regulatory and Aesthetic Guidelines for Calcium Levels
Despite the lack of a universal health standard, several organizations provide guidelines based on aesthetic and operational considerations. These guidelines help consumers and water suppliers manage the non-health-related impacts of calcium.
World Health Organization (WHO) Guidelines
The WHO does not provide health-based guideline values for hardness or its components, including calcium. It notes that hard water may contribute positively to dietary calcium and magnesium intake, especially for populations with marginal mineral intake. However, the WHO acknowledges that hardness levels above 500 mg/L as $CaCO_3$ are often considered aesthetically unacceptable due to scaling and taste issues. They have also cited research suggesting a calcium taste threshold between 100–300 mg/L.
United States Environmental Protection Agency (EPA) Classifications
The EPA does not set a mandatory health standard for hardness but offers a classification system based on total calcium carbonate concentration.
Health Canada and Other Standards
Canadian guidelines have set a Health-Based Value (HBV) of 300 mg/L for calcium, primarily related to an elevated risk of kidney stone formation. They do not, however, establish a Maximum Acceptable Concentration (MAC) for calcium, as levels are typically below the HBV. This demonstrates a proactive, though not mandatory, approach to setting advisory levels based on potential long-term risks.
The Impact of Calcium on Your Home and Health
The concentration of calcium in your drinking water has multiple effects, which can be categorized into household annoyances and health benefits.
Household and Aesthetic Effects
- Scale Buildup: High calcium levels are the primary cause of limescale, a hard, white deposit that forms on heating elements and inside pipes, reducing the efficiency and lifespan of appliances like water heaters and kettles.
- Soap Scum: Calcium reacts with soap to form an insoluble residue, or scum, which reduces the soap's ability to lather and clean effectively. This leads to spotty dishes and clothes that feel dingy.
- Taste and Appearance: While higher concentrations of calcium can be acceptable, levels above a certain threshold can impart a noticeable, sometimes unpleasant, chalky taste to water.
Health Benefits of Hard Water
Despite the aesthetic issues, hard water is not only safe but can be beneficial to health.
- Dietary Contribution: Hard water can contribute positively to overall mineral intake, especially for calcium and magnesium. For individuals with a low intake of these minerals from food, drinking hard water can help supplement their diet.
- Cardiovascular Health: Some studies have suggested a weak inverse correlation between water hardness and cardiovascular health, possibly due to the beneficial properties of calcium and magnesium.
- Bone Health: The calcium absorbed from water, particularly from some mineral waters, can be as bioavailable as calcium from dairy, supporting bone health.
Water Hardness Level Comparison
| Classification | WHO Guideline (as $CaCO_3$ mg/L) | EPA Guideline (as $CaCO_3$ mg/L) | Health Canada (HBV for Calcium only mg/L) |
|---|---|---|---|
| Soft | Generally < 100 | 0–60 | N/A |
| Moderately Hard | 100–200 | 61–120 | N/A |
| Hard | 200–300 | 121–180 | N/A |
| Very Hard | > 300 | > 180 | N/A |
| Health-Based Value | Not set | Not set | 300 |
| Aesthetic Limit | > 500 | N/A | N/A |
Effective Calcium Removal Methods
For those concerned about the aesthetic or operational issues of hard water, several treatment options can effectively reduce calcium levels. The best choice depends on your specific needs and budget.
Common Removal Systems
- Water Softeners (Ion Exchange): This is the most common method for whole-house treatment. It works by passing water through a resin bed that replaces calcium and magnesium ions with sodium or potassium ions. While effective against scaling, it does add sodium to the water, which may be a concern for those on low-sodium diets.
- Reverse Osmosis (RO): RO systems use a semipermeable membrane to remove up to 99% of dissolved solids, including calcium. These are typically installed at a single tap (Point-of-Use) for drinking and cooking water. RO water is very pure but can taste bland due to the removal of all minerals.
- Distillation: This process involves boiling water and condensing the steam, leaving all minerals, including calcium, behind. It is highly effective but slow, energy-intensive, and removes all minerals, leaving the water flat-tasting.
Conclusion
In summary, there is no official, health-based standard for calcium in drinking water because hard water is generally considered safe and can even provide beneficial dietary minerals. The concentration of calcium is primarily a concern for its contribution to water hardness, which causes aesthetic issues like scaling and reduced soap effectiveness. Organizations like the WHO and EPA offer guidelines based on these non-health factors, helping consumers and water systems manage water quality for optimal taste and appliance longevity. Ultimately, the decision to treat water for high calcium levels is a matter of personal preference, not a health necessity. Consumers should test their water to understand its hardness level and choose a treatment method, such as an ion exchange water softener or a reverse osmosis system, if they wish to mitigate the effects of hard water. For those with specific health concerns, it is always recommended to consult a healthcare provider.
