Reverse Osmosis (RO) is a widely adopted method for water purification, effectively removing a broad spectrum of impurities. As individuals consider RO systems, a common inquiry arises regarding the resulting water’s pH level. This article explores the pH of RO water, its influencing factors, and practical implications.
What is pH?
The term “pH” quantifies the acidity or alkalinity of a water-based substance. This measurement relies on a scale ranging from 0 to 14. A pH value of 7 signifies a neutral substance. Values below 7 indicate increasing acidity, while those above 7 denote increasing alkalinity, also known as basicity.
Each whole number change on the pH scale represents a tenfold difference in the concentration of hydrogen ions. For instance, a substance with a pH of 5 is ten times more acidic than one with a pH of 6. Understanding pH is important for assessing water quality, as it influences chemical properties, taste, and suitability for various applications.
How Reverse Osmosis Works
Reverse osmosis is a filtration process that purifies water by employing pressure. This pressure forces water molecules through a semi-permeable membrane. The membrane acts as a selective barrier, allowing water molecules to pass while retaining larger dissolved solids, contaminants, and minerals.
This method effectively removes a wide array of impurities, including salts, heavy metals, microorganisms, and chlorine. The process separates clean water from a concentrated stream of impurities. This purification results in water with significantly reduced levels of dissolved substances.
The pH of RO Water Explained
Reverse osmosis water typically exhibits a slightly acidic pH, often ranging between 5.0 and 7.0. This acidity stems from two primary factors: the removal of alkaline-forming minerals and the absorption of carbon dioxide from the air. The RO process strips out buffering minerals like calcium and magnesium, which help maintain a stable, neutral pH. Without these buffering agents, the water becomes more susceptible to pH changes.
Pure, demineralized water readily absorbs carbon dioxide (CO2). When CO2 dissolves, it forms carbonic acid (H2CO3), which lowers the water’s pH. This reaction can cause the pH of freshly produced RO water to drop from a neutral 7 to values between 5.0 and 5.5.
Several factors can influence the exact pH of RO water. The initial characteristics of the source water, such as its starting pH and mineral content, play a role in the final RO water pH. The efficiency of the RO membrane and the duration of the water’s exposure to air after filtration can also affect its pH.
Practical Considerations and pH Adjustment
Despite its slightly acidic nature, reverse osmosis water is generally considered safe for consumption by most individuals. The Environmental Protection Agency (EPA) considers drinking water with a pH between 6.5 and 8.5 safe. Many common beverages, such as coffee, fruit juice, and carbonated drinks, are significantly more acidic than RO water.
However, the pH of RO water can have practical implications in specific applications. Its low mineral content and slight acidity may contribute to the corrosion of certain metal pipes over time, potentially leading to the leaching of metals like lead and copper. For sensitive uses like aquariums, the lower pH can negatively affect aquatic life. Industrial processes often require water within a precise pH range, making pH adjustment of RO water necessary.
To adjust RO water’s pH, several methods are available. Remineralization filters are a common solution, reintroducing beneficial minerals like calcium, magnesium, and potassium to raise pH and restore buffering capacity. Other options include alkaline water pitchers or pH-balancing drops. For larger systems, CO2 degassing or blending RO water with tap water can achieve a desired pH.