What to test water for 

Some of the ways  to test water for pollutants are the pH scale ,alkalinit , hardness , nitrates , nitrites and ammonia , ortho - and total phosphates ,and dissolved oxygen and biochemical oxygen demand. The most commonly used is the pH scale which ranges from 1-14  the lowest  number is the most acidic and the highest number is the most basic . Typically streams have a pH level between 6.5-8.0 which is neutral to slightly basic . Municipal water is often pH-adjusted, in order to prevent corrosion from pipes and to prevent dissolution of lead into water supplies. During water treatment pH adjustments may also be required. The pH is brought up or down through addition of basics or acids. An example of lowering the pH is the addition of hydrogen chloride, in case of a basic liquid. An example of bringing up the pH is the addition of natrium hydroxide, in case of an acidic liquid.The pH will be converted to approximately seven to seven and a half, after addition of certain concentrations of acids or basics. The concentration of the substance and the kind of substance that is added, depend upon the necessary decrease or increase of the pH.

Some more chemicals  used for treatment

For the chemical treatment of water a great variety of chemicals can be applied. Below, the different types of water treatment chemicals are summed up. 
• Algaecides
• Antifoams
• Biocides
• Boiler water chemicals
• Coagulants
• Corrosion inhibitors
• Disinfectants
• Flocculants
• Neutralizing agents
• Oxidants
• Oxygen scavengers
• pH conditioners
• Resin cleaners
• Scale inhibitors