The cleanliness of water depends entirely on its intended use. Safety standards differ for drinking water, irrigation, and industrial applications, and many impurities lack defined standards. To purify water, various treatment methods are employed, sometimes in stages. These include settling and skimming, boiling and condensation, adding chemicals to kill or capture contaminants, and filtering through membranes. However, each process incurs costs, from energy and chemicals to equipment and labor. Additionally, disposing of the removed contaminants can be expensive and pose environmental challenges. Ultimately, achieving “clean enough” water requires balancing the desired purity level with the practical and financial constraints of treatment.