Alkaline water has an elevated pH level, typically ranging from 8 to 10, which is higher than the neutral pH of 7 found in regular tap water. This alkalinity is achieved through ionization or the addition of minerals like calcium and magnesium. Storing this high-pH water in plastic bottles raises concerns about the chemical stability of the container material. Proper storage is necessary to maintain the water’s properties and prevent unwanted substances from leaching from the plastic.
How High pH Water Interacts with Plastics
Storing any liquid in plastic involves a potential chemical interaction, and alkaline water introduces an accelerating factor known as alkaline hydrolysis. This process promotes the breakdown of the long polymer chains that make up the plastic material. While degradation is normally slow, the presence of a higher pH acts as a catalyst, especially when combined with heat or prolonged storage.
As the polymer structure breaks down, it increases the likelihood of releasing trace chemicals into the stored water. These chemicals often include plasticizers like phthalates or bisphenol compounds, such as BPA or BPS. This chemical principle applies to consumer-grade storage, meaning the risk of leaching is elevated compared to storing neutral water. Over time, this interaction compromises the integrity of the container and the purity of the water.
Evaluating Different Types of Plastic Containers
The chemical stability of plastic depends on its specific polymer composition, identified by the Resin Identification Code (RIC) found on the container. Polyethylene Terephthalate, or PET (RIC 1), is the most common plastic for single-use water bottles but exhibits limited stability in highly alkaline conditions. PET is recommended only for liquids with a pH range between 4 and 9, making it a poor choice for alkaline water storage, particularly for periods longer than a few days.
In contrast, High-Density Polyethylene (HDPE, RIC 2) and Polypropylene (PP, RIC 5) offer greater resistance to alkaline substances. These materials are widely used for containers that hold harsher alkaline products, such as detergents or household cleaners, demonstrating their stability against bases. HDPE and PP are considered the safest plastic options for short-term alkaline water use.
They are less prone to degradation and are not known to contain bisphenol compounds like BPA in their primary formulation. Consumers should remain cautious with plastics labeled “BPA-free,” as these often use alternatives like BPS, which are also under scrutiny for potential endocrine-disrupting properties. While HDPE and PP are better choices than PET, the extended contact time and the higher pH still introduce a continuous risk. Therefore, any plastic container used for alkaline water should be replaced frequently and never exposed to high temperatures, such as those found in a hot car or dishwasher.
Recommended Long-Term Storage Solutions
To bypass the risk of chemical leaching and polymer degradation, non-plastic alternatives are the superior choice for long-term alkaline water storage. Borosilicate glass is the gold standard because it is chemically inert and non-porous, meaning it will not react with the alkaline water or leach any compounds. Its resistance to thermal shock also makes it durable for everyday use and cleaning.
Another excellent alternative is high-grade stainless steel, specifically 304 or 316 food-grade material. Stainless steel is highly resistant to corrosion in alkaline environments, making it a safe choice for prolonged contact with high-pH water.
Water quality is best maintained by storing containers in a cool, dark location away from direct sunlight and heat, which helps preserve the water’s pH and antioxidant potential. Ensuring the container is tightly sealed minimizes air exposure, preventing the water’s alkalinity from decreasing over time due to the absorption of carbon dioxide.