References
1. Smith, J. A., & Brown, L. M. "Water Softening Techniques: A Comprehensive Review." *Journal of Environmental Chemistry*, 15(3), 123-135.
2. White, R. H. "Ion Exchange Resins: Properties and Applications." *Academic Press*.
3. American Public Health Association (APHA). "Standard Methods for the Examination of Water and Wastewater." 23rd ed.
4. Wilson, K. S., & Johnson, P. Q. "Principles of Water Treatment." *Wiley*.
5. Resin Manufacturer's Name. "Ion Exchange Resin User Manual."