Here is a list of over 100 major chemicals used in water treatment, along with a brief description of their applications:

1. Chlorine: Used as a disinfectant to kill bacteria, viruses, and other pathogens in water.
2. Chlorine Dioxide: Used for disinfection and oxidation of organic matter in water treatment.
3. Sodium Hypochlorite: Used as a disinfectant and oxidizing agent in water treatment.
4. Calcium Hypochlorite: Used for disinfection and oxidation in water treatment processes.
5. Sodium Dichloroisocyanurate (SDIC): Used as a disinfectant in water treatment.
6. Poly Aluminum Chloride (PAC): Used as a coagulant for solid particle removal in water.
7. Aluminum Sulfate: Used as a coagulant for turbidity and solid removal in water treatment.
8. Ferric Chloride: Used as a coagulant and flocculant in water treatment processes.
9. Ferrous Sulfate: Used as a coagulant and pH adjuster in water treatment.
10. Activated Carbon: Used for the removal of organic contaminants and taste/odor control.
11. Powdered Activated Carbon (PAC): Used for adsorption of organic matter in water treatment.
12. Granular Activated Carbon (GAC): Used for adsorption of organic compounds in water.
13. Anthracite: Used as a filter media for the removal of suspended solids in water.
14. Sand: Used as a filter media for the removal of sediment and suspended particles.
15. Gravel: Used as a support media in water filtration systems.
16. Zeolite: Used as a filter media for ion exchange and ammonia removal in water treatment.
17. Ion Exchange Resins: Used for water softening and removal of specific ions.
18. Sodium Hydroxide: Used for pH adjustment and water alkalinity control.
19. Sulfuric Acid: Used for pH adjustment and water acidity control.
20. Sodium Carbonate: Used for pH adjustment and water alkalinity control.
21. Sodium Bicarbonate: Used for pH adjustment and buffering in water treatment.
22. Lime (Calcium Hydroxide): Used for pH adjustment and precipitation of impurities.
23. Sodium Bisulfite: Used for dechlorination and removal of excess chlorine in water.
24. Activated Alumina: Used for fluoride removal from water.
25. Greensand: Used for the removal of iron and manganese from water.
26. Hydrogen Peroxide: Used for oxidation and disinfection in water treatment processes.
27. Potassium Permanganate: Used for oxidation and removal of organic compounds.
28. Sodium Bisulfate: Used for dechlorination and pH adjustment in water treatment.
29. Sodium Thiosulfate: Used for dechlorination and reduction of chlorine in water.
30. Calcium Carbonate: Used for pH adjustment and remineralization of water.
31. Sodium Hexametaphosphate: Used for sequestering and scale inhibition in water treatment.
32. Polyphosphates: Used for sequestering and scale inhibition in water treatment processes.
33. Sodium Silicate: Used for corrosion control and as a coagulant aid in water treatment.
34. Sodium Tripolyphosphate: Used as a sequestering agent and detergent builder in water treatment.
35. Sodium Polyphosphate: Used as a sequestering agent and scale inhibitor in water treatment.
36. Sodium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment.
37. Potassium Permanganate: Used for oxidation and removal of organic compounds in water.
38. Sodium Hydrogen Carbonate: Used for pH adjustment and buffering in water treatment.
39. Potassium Hydrogen Carbonate: Used for pH adjustment and buffering in water treatment processes.
40. Sodium Sulfite: Used for dechlorination and removal of excess chlorine in water.
41. Potassium Sulfite: Used for dechlorination and removal of excess chlorine in water treatment.
42. Calcium Sulfite: Used for dechlorination and removal of excess chlorine in water.
43. Magnesium Sulfite: Used for dechlorination and removal of excess chlorine in water treatment.
44. Sodium Bisulfate: Used for pH adjustment and acidity control in water treatment processes.
45. Potassium Bisulfate: Used for pH adjustment and acidity control in water treatment.
46. Calcium Bisulfate: Used for pH adjustment and acidity control in water treatment processes.
47. Sodium Fluoride: Used for fluoridation of drinking water.
48. Sodium Chlorite: Used for disinfection and oxidation in water treatment processes.
49. Potassium Chlorite: Used for disinfection and oxidation in water treatment.
50. Sodium Chlorate: Used for disinfection and oxidation in water treatment processes.
51. Potassium Chlorate: Used for disinfection and oxidation in water treatment.
52. Sodium Hydrogen Sulfite: Used for dechlorination and removal of excess chlorine in water.
53. Sodium Nitrite: Used for corrosion inhibition in water treatment.
54. Sodium Hexametaphosphate: Used for sequestering and scale inhibition in water treatment.
55. Sodium Polyacrylate: Used as a scale inhibitor and dispersant in water treatment processes.
56. Sodium Hydroxymethanesulfonate: Used as a reducing agent and oxygen scavenger in water treatment.
57. Sodium Phosphate: Used for sequestering, pH adjustment, and corrosion control in water treatment.
58. Sodium Metabisulfite: Used for dechlorination and reducing agent in water treatment.
59. Potassium Metabisulfite: Used for dechlorination and reducing agent in water treatment processes.
60. Calcium Metabisulfite: Used for dechlorination and reducing agent in water treatment.
61. Magnesium Sulfate: Used for hardness adjustment and as a coagulant aid in water treatment.
62. Sodium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment.
63. Potassium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment processes.
64. Calcium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment.
65. Magnesium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment processes.
66. Sodium Bromide: Used for disinfection and as a biocide in water treatment.
67. Calcium Bromide: Used for disinfection and as a biocide in water treatment processes.
68. Sodium Bisulfate: Used for pH adjustment and acidity control in water treatment.
69. Potassium Bisulfate: Used for pH adjustment and acidity control in water treatment processes.
70. Calcium Bisulfate: Used for pH adjustment and acidity control in water treatment.
71. Magnesium Bisulfate: Used for pH adjustment and acidity control in water treatment processes.
72. Sodium Fluorosilicate: Used for fluoridation of drinking water and as a corrosion inhibitor.
73. Potassium Fluorosilicate: Used for fluoridation of drinking water and as a corrosion inhibitor in water treatment.
74. Sodium Metasilicate: Used for pH adjustment and as a detergent builder in water treatment.
75. Sodium Dithionite: Used as a reducing agent and oxygen scavenger in water treatment.
76. Potassium Dithionite: Used as a reducing agent and oxygen scavenger in water treatment processes.
77. Sodium Sulphate: Used for pH adjustment and as a coagulant aid in water treatment.
78. Potassium Sulphate: Used for pH adjustment and as a coagulant aid in water treatment processes.
79. Calcium Sulphate: Used for pH adjustment and as a coagulant aid in water treatment.
80. Magnesium Sulphate: Used for pH adjustment and as a coagulant aid in water treatment processes.
81. Sodium Bisulfite: Used for dechlorination and removal of excess chlorine in water.
82. Potassium Bisulfite: Used for dechlorination and removal of excess chlorine in water treatment.
83. Calcium Bisulfite: Used for dechlorination and removal of excess chlorine in water treatment processes.
84. Magnesium Bisulfite: Used for dechlorination and removal of excess chlorine in water.
85. Sodium Hexametaphosphate: Used for sequestering and scale inhibition in water treatment.
86. Sodium Polyacrylate: Used as a scale inhibitor and dispersant in water treatment processes.
87. Sodium Hydroxymethanesulfonate: Used as a reducing agent and oxygen scavenger in water treatment.
88. Sodium Phosphate: Used for sequestering, pH adjustment, and corrosion control in water treatment.
89. Sodium Metabisulfite: Used for dechlorination and reducing agent in water treatment.
90. Potassium Metabisulfite: Used for dechlorination and reducing agent in water treatment processes.
91. Calcium Metabisulfite: Used for dechlorination and reducing agent in water treatment.
92. Magnesium Sulfate: Used for hardness adjustment and as a coagulant aid in water treatment.
93. Sodium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment.
94. Potassium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment processes.
95. Calcium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment.
96. Magnesium Nitrate: Used for corrosion inhibition and as an oxidizing agent in water treatment processes.
97. Sodium Bromide: Used for disinfection and as a biocide in water treatment.
98. Calcium Bromide: Used for disinfection and as a biocide in water treatment processes.
99. Sodium Bisulfate: Used for pH adjustment and acidity control in water treatment.
100. Potassium Bisulfate: Used for pH adjustment and acidity control in water treatment processes.

Please note that this list is not exhaustive, and the usage of specific chemicals may vary depending on the water source, treatment objectives, and regulatory requirements in different regions. It’s important to consult with water treatment professionals and adhere to local guidelines when selecting and using water treatment chemicals.