Certified Facility Manager (CFM) Practice Exam

When water has high 'hardness,' what percentage is typically replaced to soften it?

1. 20%

2. 50%

3. 80%

4. 100%

The correct answer is: 50%

Water hardness is primarily caused by the presence of dissolved calcium and magnesium ions. When the goal is to soften water, a water treatment process is typically utilized, such as ion exchange or reverse osmosis. Replacing about 50% of the water with softer water effectively reduces the overall concentration of hardness-causing minerals. This percentage strikes a balance between managing operational costs and achieving a significant reduction in hardness. Since complete replacement could lead to high expenses and potential water source issues, 50% replacement is often a practical approach for maintaining acceptable water quality without excessive resource expenditure. The other percentages, such as 20% or 80%, may not efficiently lower hardness to the desired levels or may introduce complications in a facility's water management system. For instance, replacing too little may not yield the desired outcomes, while replacing too much could lead to unnecessary resource use and financial burden. Therefore, replacing about half of the water is recognized as an effective and pragmatic strategy in managing water hardness levels.