Title: PH
Content:   In chemistry, pH (, historically denoting "potential of hydrogen" (or “power of hydrogen") is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of H+ ions) are measured to have lower pH values than basic or alkaline solutions. The pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in the solution. This is because the formula used to calculate pH approximates the negative of the base 10 logarithm (i.e. the decimal cologarithm) of the molar concentration of hydrogen ions in the solution. More precisely, pH is the negative of the base 10 logarithm of the activity of the H+ ion. At 25 °C, solutions with a pH less than 7 are acidic, and solutions with a pH greater than 7 are basic. Solutions 
Title: PH
Content:  Pure water is neutral. When an acid is dissolved in water, the pH will be less than 7 (25 °C). When a base, or alkali, is dissolved in water, the pH will be greater than 7. A solution of a strong acid, such as hydrochloric acid, at concentration 1 mol dm−3 has a pH of 0. A solution of a strong alkali, such as sodium hydroxide, at concentration 1 mol dm−3, has a pH of 14. Thus, measured pH values will lie mostly in the range 0 to 14, though negative pH values and values above 14 are entirely possible. Since pH is a logarithmic scale, a difference of one pH unit is equivalent to a tenfold difference in hydrogen ion concentration. The pH of neutrality is not exactly 7 (25 °C), although this is a good approximation in most cases. Neutrality is defined as the condition where [H+] 
Title: PH
Content:  a pH of 7 at this temperature are neutral (e.g. pure water). The neutral value of the pH depends on the temperature – being lower than 7 if the temperature increases. The pH value can be less than 0 for very strong acids, or greater than 14 for very strong bases. The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode. The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or a color-changing indicator. Measurements of pH are important in chemistry, agronomy, medicine, water treatment, and many other applications.
Title: ISO 31-8
Content:  pH is a quantity of dimension 1, that is it has no unit. Values pH(S) for a range of standard solutions S are listed in Definitions of pH scales, standard reference values, measurement of pH, and related terminology. Pure Appl. Chem. (1985), 57, pp 531–542, where further details can be found. pH has no fundamental meaning; its official definition is a practical one. However, in the restricted range of dilute aqueous solutions having amount-of-substance concentrations less than 0.1 mol/L, and being neither strongly alkaline nor strongly acidic (2 < pH < 12), the definition is such that  where c(H+) denotes the amount-of-substance concentration of hydrogen ion H+ and y1 denotes the activity coefficient of a typical uni-univalent electrolyte in the solution.
Title: PH
Content: [H+]T = [H+]F + [HSO] [H+]F = [H+]T − [HSO] = [H+]T ( 1 + [SO] / K )−1 [H+]SWS = [H+]F + [HSO] + [HF] pHF = − log [H+]F ; pHT = − log ( [H+]F + [HSO] ) = − log [H+]T ; pHSWS = − log ( [H+]F + [HSO] + [HF] ) = − log [H+]SWS The pH of seawater is typically limited to a range between 7.4 and 8.5. It plays an important role in the ocean's carbon cycle, and there is evidence of ongoing ocean acidification caused by carbon dioxide emissions. However, pH measurement is complicated 
Title: Hydronium
Content: H2O <-> OH- + H+ The concentration of H+ ions determines a solution's pH. The concentration of hydroxide ions determines a solution's pOH. The molecules in pure water auto-dissociate into aqueous protons and hydroxide ions in the following equilibrium:  In pure water, there is an equal number of hydroxide and H+ ions, so it is a neutral solution. At 25 C, water has a pH of 7 and a pOH of 7 (this varies when the temperature changes: see self-ionization of water). A pH value less than 7 indicates an acidic solution, and a pH value more than 7 indicates a basic solution.
Title: PH meter
Content:   A pH meter is a scientific instrument that measures the hydrogen-ion activity in water-based solutions, indicating its acidity or alkalinity expressed as pH. The pH meter measures the difference in electrical potential between a pH electrode and a reference electrode, and so the pH meter is sometimes referred to as a "potentiometric pH meter". The difference in electrical potential relates to the acidity or pH of the solution. The pH meter is used in many applications ranging from laboratory experimentation to quality control.
Title: Water purification
Content:  Pure water has a pH close to 7 (neither alkaline nor acidic). Sea water can have pH values that range from 7.5 to 8.4 (moderately alkaline). Fresh water can have widely ranging pH values depending on the geology of the drainage basin or aquifer and the influence of contaminant inputs (acid rain). If the water is acidic (lower than 7), lime, soda ash, or sodium hydroxide can be added to raise the pH during water purification processes. Lime addition increases the calcium ion concentration, thus raising the water hardness. For highly acidic waters, forced draft degasifiers can be an effective way to raise the pH, by stripping dissolved carbon dioxide from the water. Making the water alkaline helps 
Title: Alkali soil
Content: → 2 + Notes: ; Water (H2O) is partly dissociated into H3O+ (hydronium) and OH– (hydroxyl) ions. The ion H3O+ has a positive electric charge (+) and its concentration is usually written as [H+]. The hydroxyl ion OH– has a negative charge (−) and its concentration is written as [OH−]. ; In pure water, at 25 °C, the dissociation constant of water (Kw) is 10−14. In neutral water, the pH, being the negative decimal logarithm of the H3O+ concentration, it is 7. Similarly, the pOH is also 7. Each unit decrease in pH indicates a tenfold increase of the H3O+ concentration. Similarly, each unit increase in pH indicates a 
Title: Wastewater discharge standards in Latin America
Content:  The pH is a chemical parameter that measures the acidity or basicity of the water and is commonly measured in situ. Distilled water has a pH of 7, where less than 7 is considered acid and greater than 7 is considered basic. In most cases, low pH is due to organic overloading and low oxygen conditions in the water. This characteristic is strictly controlled because it has a direct effect on water ecosystems and sewer systems materials. Usually, pH standard is between 6 and 9 and can vary easily depending on the discharge content. In this case, Peru was the country with the smallest range (6–8) and Argentina and Mexico were the ones with the widest range (5.5–10). No limit was found for Canada Regulation.

Question: what is the definition of ph in water?
Answer: potential of hydrogen.