pH is a measure of the hydrogen ion activity in a solution. Pure water that contains an equal balance of positive hydrogen ions (H+) and negative hydroxide ions (OH-) has a neutral pH.
Solutions with a higher concentration of hydrogen ions (H+) than pure water are acidic and have a pH less than 7.
Solutions with a higher concentration of hydroxide ions (OH-) than water are basic (alkaline) and have a pH greater than 7.
Featured pH/ORP Analyzers and Testing Products
Portable pH Meters
Simple and affordable pH measurement for home, school, and hobbyist use. Hach's pH testers deliver quick and easy measurements with accurate and reliable results. We also offer pH buffer solutions for our testers.
Accurate and precise pH measurement for laboratory and industrial applications. Hach's benchtop pH meters offer advanced features and user-friendly interfaces.
Ensure consistent pH control with Hach's reliable suite of controllers and transmitters. Choose from our range of automated solutions for various applications.
Simple and affordable pH measurement for home, school, and hobbyist use. Hach's pH testers deliver quick and easy measurements with accurate and reliable results.
Take the guesswork out of pH testing with Hach's pH test strips. Our high-quality strips provide quick and dependable readings for a variety of applications.
pH of drinking water is measured at multiple stages in a drinking water plant. Normal pH range for tap water is 6.5-8.5 throughout both treatment process and distribution. Drinking water pH level must be monitored to minimize corrosion, contamination and adverse effects on taste, odor, color and appearance.
pH adjustment is necessary for the precipitation of heavy metals in wastewater plants. In biological treatment processes, pH can affect the microorganism metabolizing waste. If the pH is too high or low in aeration basins, the microorganisms lose the ability to convert waste to energy and raw materials. Monitoring pH is helpful for nitrifying systems as too high or too low pH can inhibit the nitrifying bacteria and lead to process upsets.
Anaerobic digesters must maintain a balance between several microbial populations. If the pH increases outside of acceptable limits, methane production stops and the digester system will fail. To comply with regulation pH must be measured in effluent. Facilities must abide by the National Pollutant Discharge Elimination System - NPDES.
Proper pH balance is critical to overall boiler chemistry at nearly every stage to maintaining high purity water. pH is an important factor in monitoring the corrosive properties of water, which can damage equipment.
This method uses a pH sensing system (including a pH meter, a pH sensing electrode and a pH reference electrode) to take an electrochemical measurement to precisely determine where the tested fluid falls on the pH scale.
Advantages
This is the most accurate method for pH measurement. Portable, lab or process/online options are available for this method. This method can be ISO approved for monitoring pH.
Disadvantages
This method requires proper handling, care and maintenance of the pH probe and involves higher instrument costs.
Our online technology course provides more information on the importance of monitoring and measuring pH.
An indicator solution changes color when added to the solution being tested. That color change is then visually compared against a color chart to determine pH.
Advantages
This method is simple, inexpensive and portable.
Disadvantages
Solutions being tested with this method must be free of color and have no turbidity. Solutions being tested with this method must not have a secondary reaction with the indicator solution. No online or process options exist for this method. This method does not produce exact measurements.
Liquid Indicator Dyes
Liquid dyes are added directly to the solution to produce a color change that indicates changing pH.
Dye-infused paper strips are dipped into a solution and then change color to indicate corresponding pH. This method is not affected by color or turbidity in a sample.
Like the visual method used in test strips and color wheels, an indicator solution is used to create a color change in the solution being tested. However, with this method the color change is not assessed by the human eye, it is measured by a photometer (colorimeter or spectrophotometer) to produce a more precise pH reading.
Advantages
This method is portable, removes the subjectivity of the human eye and does not require complex pH meter calibration.
Disadvantages
Solutions being tested with this method must be colorless. No online/process options exist for this method and there are costs associated with instruments.
Frequently Asked Questions
pH measurement is a key step in many water testing and purification processes:
A change in the pH of water can alter the behavior of chemicals in the solution.
pH may affect product quality and consumer safety. Changes in pH can alter flavor, color, shelf-life, product stability and other characteristics.
Low pH of tap water can cause corrosion in the distribution system and can allow harmful heavy metals to leach out, while high pH may lead to scaling.
Managing industrial water pH helps maintain process stability, prevent corrosion and damage to equipment.
In natural environments, pH swings can affect aquatic plants and animals.
Hach® offers the testing equipment, resources, training and software to successfully monitor and maintain pH in a wide array of process applications.
pH is a critical water quality indicator. There are several common techniques available for measuring pH: titrimetric, colorimetric, litmus paper and electrochemical. There are a variety of process and laboratory electrochemical pH sensors, including those built on combination and differential technologies (pHD sensor). The most common and accurate pH measurement technique is by electrochemical combination electrode. A combination pH electrode responds to the hydrogen ion (H+) concentration (activity) by developing an electrical potential across the electrode bulb/water interface. This potential difference is measured with a voltmeter. Electrodes are designed for optimal performance in various matrices. Hach HQD® Meters and a versatile assortment of IntelliCAL® Probes bring simplicity and consistency to pH measurements in any matrix. See the following document for more information.
When testing the pH of soil-based samples, it is advisable to use a pH probe with a strong glass tip and high electrolyte outflow. Mix 5 grams of the soil sample with 25 grams of deionized water while stirring carefully. Let the mixture stand without stirring for 10 minutes to separate the particles from the liquid. Insert the pH probe in such a way that the glass bulb is totally covered by particles but the diaphragm is not. Wait for a stable reading.
A pH meter and electrode such as an HQ Series meter and probe must be used if your results need to be reported to an agency. You can review the Hach USEPA pH electrode Method 8156 for additional information or reference the DIN EN ISO 10523 for additional information.
pH meters will give the best accuracy and sensitivity, measure across the full pH range and can be used with most water samples compared to colorimetric or test strip measurements. However, they require regular calibration with pH buffer solutions. Hach has several different kits available, complete with calibration buffers for simplified measurement solutions, as well as online sensors that can be placed in the water stream.
