簡介
水的 pH 值經常是民眾關心飲用水品質的重點。在香港，許多人可能會感到疑惑，為什麼蒸餾水的 pH 值通常低於 6 (稍微呈酸性)，但是香港的自來水 pH 值卻通常高於 7.5 (呈鹼性)。根據香港水務署 (WSD) 標準，香港自來水的pH值應在 6.5 到 9.5 的範圍內。這是否意味著飲用pH值低於 6 的水是不安全的？這篇網誌將解釋這些差異背後的原因，以及為什麼人們不應該擔心他們飲用pH值低於 6 的蒸餾水。我們還將討論水的pH值如何影響人類健康。
認識 pH：科學快速入門
pH 值的範圍從 0 到 14，其中 7 為中性。pH 值低於 7 被視為酸性，而高於 7 則是鹼性。純水的理想 pH 值為 7，但這個值可能因環境因素與溶解物質的存在而改變。
常見例子：
- 檸檬汁：pH 大約 2（酸性）
- 香港的自來水：pH 7.5 至 9（鹼性）
- 蒸餾水：通常介於 5.5 到 6（輕微酸性）
為什麼蒸餾水的 pH 值低於 6？
蒸餾水是透過將水煮沸，將蒸氣冷凝回液態，去除幾乎所有雜質與礦物質而製成。雖然這個過程產生接近純 H₂O 的水，但有幾個因素會導致其 pH 值略低於 7：
吸收空氣中的二氧化碳（CO₂）：
蒸餾水由於缺乏礦物質與雜質，因此對溶解氣體的吸附能力很強。當暴露在空氣中時，它會吸收二氧化碳，二氧化碳與水反應生成碳酸（H₂CO₃）：
CO₂ + H₂O → H₂CO₃
這種弱酸在水中會稍微解離，導致 pH 值下降到大約 5.5 到 6。
缺乏緩衝礦物質：自來水含有鈣和鎂等礦物質，有助於緩衝pH值的變化。蒸餾水缺乏這些礦物質，使其更容易受到外部因素影響而產生pH值變化。
為甚麼香港自來水呈鹼性？
香港的自來水通常具有較高於 7.5 的pH值，原因如下：
水處理做法：香港水務署 (WSD) 在處理過程中調整自來水的pH值，以防止管道銹蝕。保持鹼性pH有助於保護水配送系統免受鐵銹和金屬滲出的影響。
礦物含量：香港的自來水含有天然礦物質，例如鈣和鎂，這些礦物質有助於其呈鹼性。
水源：香港的一大部分水來自中國大陸的東江，該地區因地質而自然具有較高的pH值。
當飲用水的 pH 值低於 6 時，您應該擔心嗎？
如飲用的是蒸餾水，是不需要擔心的。雖然蒸餾水的 pH 值通常低於 6，但這並不會對健康構成風險。原因如下：
水務署 pH 標準：根據香港水務署 (WSD) 的標準，飲用水的可接受 pH 範圍是 6.5 至 9.5，但這標準僅適用於自來水，不適用於蒸餾水。
人體的自然 pH 調節：人體會嚴格調節其內部 pH，特別是血液 pH，保持在約 7.4。您飲用的水的 pH 對這種平衡影響甚微。
口腔內的暫時性 pH 變化：飲用略酸性的水（如蒸餾水）可能會暫時降低口腔內的 pH，但這並不會造成危害，除非長期暴露。
然而，如果自來水的 pH 值低於 6.5，這可能是一個值得關注的問題。這可能表明外部來源的雜質進入了水箱或管道，導致水的 pH 值下降。
微酸水對人體健康的影響
牙齒和口腔健康： 酸性飲料（如汽水）會隨時間侵蝕琺瑯質。然而，蒸餾水的輕微酸性不足以造成損害。
消化健康： 您的胃自然會產生鹽酸（HCl），其 pH 值約為 1.5 至 3。即使您飲用略酸性的水，與胃中的酸性相比，這也是微不足道的。
雖然蒸餾水的輕微酸性無害，但您不應僅依賴蒸餾水。與提供鈣和鎂等必需礦物質的自來水不同，蒸餾水缺乏這些礦物質，導致礦物質攝取量減少。
總結
了解蒸餾水和自來水之間的 pH 差異可以幫助減輕對飲用水質量的擔憂。由於吸收二氧化碳，蒸餾水的 pH 可能低於 6，但這完全正常，並不會對健康構成威脅。關鍵是要飲用多種水源 (如礦泉水或自來水) 以滿足身體的礦物質需求和保持水分攝取。
這篇文章是利用人工智能幫助撰寫的。
English Version
Introduction
Water pH is often a topic of concern when it comes to drinking water safety and quality. Many people in Hong Kong may be puzzled when they discover that distilled water often has a pH below 6, which is slightly acidic, while tap water in Hong Kong usually has a pH above 7.5, making it alkaline. According to the WSD standard, tap water should have a pH within the range of 6.5 to 9.5. Does this mean that drinking water with a pH below 6 is unsafe? This blog will explain the reasons behind these differences and why people should not worry if the pH of their drinking distilled water falls below 6. We will also discuss how water pH affects human health.
Understanding pH: A Quick Science Refresher
The pH scale ranges from 0 to 14, with 7 being neutral. A pH below 7 is considered acidic, while a pH above 7 is alkaline. Pure water ideally has a pH of 7. However, this can change depending on environmental factors and the presence of dissolved substances.
Common Examples:
Lemon juice: pH around 2 (acidic)
Tap water in Hong Kong: pH 7.5 to 9 (alkaline)
Distilled water: often between 5.5 and 6 (slightly acidic)
Why is the pH of Distilled Water Below 6?
Distilled water is produced by boiling water and condensing the steam back into liquid form, removing almost all impurities and minerals. Although this process creates water that is nearly pure H₂O, several factors cause its pH to drop slightly below 7:
Absorption of Carbon Dioxide from the Air: Distilled water is very "hungry" for dissolved gases since it has no minerals or impurities. When exposed to air, it absorbs carbon dioxide (CO₂), which reacts with water to form carbonic acid (H₂CO₃):
CO₂ + H₂O → H₂CO₃
This weak acid dissociates slightly in water, leading to a decrease in pH, typically to around 5.5 to 6.
Lack of Buffering Minerals: Tap water contains minerals such as calcium and magnesium that help buffer pH changes. Distilled water lacks these minerals, making it more susceptible to pH changes from external factors.
Why is Hong Kong Tap Water Alkaline?
Hong Kong's tap water usually has a pH above 7.5 due to the following factors:
Water Treatment Practices: The Water Supplies Department (WSD) of Hong Kong adjusts the pH of tap water during the treatment process to prevent pipe corrosion. Maintaining an alkaline pH helps protect water distribution systems from rust and metal leaching.
Mineral Content: Tap water in Hong Kong contains natural minerals such as calcium and magnesium, which contribute to its alkaline nature.
Water Sources: A significant portion of Hong Kong’s water comes from Dongjiang River in mainland China, which naturally has a higher pH due to the geology of the region.
Should You Worry if the pH of Your Drinking Water is Below 6?
The answer is no if you are drinking distilled water. While the pH of distilled water is often below 6, it does not pose any health risks. Here's why:
WSD pH Standards: According to the Water Supplies Department of Hong Kong, the acceptable pH range for drinking water is 6.5 to 9.5, which is the reference value for tap water only and does not apply to distilled water.
Body's Natural pH Regulation: The human body tightly regulates its internal pH, particularly blood pH, which remains around 7.4. The pH of the water you drink has minimal impact on this balance.
Temporary pH Changes in the Mouth: Drinking slightly acidic water like distilled water may temporarily lower the pH in your mouth, but this is not harmful unless there is prolonged exposure.
However, if the pH of tap water falls below 6.5, it could be a cause for concern. This may indicate that impurities from external sources are entering the water tanks or pipes, leading to a decrease in the water's pH.
Impact of Slight Acidic Water on Human Health
Teeth and Oral Health:
Acidic beverages (like sodas) can erode tooth enamel over time. However, the slight acidity of distilled water is not strong enough to cause damage.
Digestive Health:
Your stomach naturally produces hydrochloric acid (HCl) with a pH of around 1.5 to 3. Even if you consume slightly acidic water, it is negligible compared to the acidity in your stomach.
Although the slight acidity of distilled water is harmless, you should not rely solely on it. Unlike tap water, which provides essential minerals like calcium and magnesium, distilled water lacks these minerals, leading to lower mineral intake.
Conclusion
Understanding the pH differences between distilled and tap water can help alleviate concerns about drinking water quality. While distilled water may have a pH below 6 due to carbon dioxide absorption, this is entirely normal and not a cause for health concerns. The key is to drink a variety of water sources (such as mineral water or tap water) to meet your body's mineral needs and maintain hydration.
This article is written with the help of AI.
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