Lime-soda ash softening can reduce water hardness to approximately which range?

• A. 10-20
• B. 30-40
• C. 40-70
• D. 300-400

Answer: (B)

Lime-soda ash softening removes calcium and magnesium hardness by raising pH and precipitating those ions as carbonates and hydroxides. In practice, this treatment typically brings finished water hardness down to about 30–40 mg/L as CaCO3, though the exact value depends on the starting hardness and the amount of chemicals used. This range reflects a balance between effective hardness removal and maintaining adequate alkalinity and sludge control.

Seeing a hardness of 10–20 mg/L would require more aggressive or additional treatment; 40–70 mg/L is possible in some setups but is not the common target for standard lime-soda softening; 300–400 mg/L is far above what lime-soda softening would produce.