Water with a high concentration of dissolved calcium and magnesium salts is called hard water. A common sign of water hardness at home is the difficulty in forming lather with soap. In many oil fields, the available water is often quite hard.

When mixed with hard water, drilling clays have lower yields. The harder the water, the more bentonite is needed to achieve satisfactory gel mud. In some cases, chemically treating the water before mixing mud is cost-effective, but this is generally not economical. However, when multiple water sources are available for a rig, a simple test can help select the softer water.

Field engineers are aware of how anhydrite (calcium sulfate) and gypsum formations affect mud properties. Calcium contamination can also occur when drilling through cement plugs or lime-rich shales. Significant calcium contamination increases water loss and gel strength. Additionally, the high alkalinity (lime) content in cement can cause a rise in Pm (mud alkalinity), further impacting drilling fluid performance

• EDTA (Standard Versenate) solution. 0.01M (1 ml = 400 mg Ca²⁺ or 1,000 mg CaCO₃).
• Strong buffer solution (ammonium hydroxide/ammonium chloride).
• Hardness Indicator Solution (Calmagite Indicator solution.)
• Titration dish, 100 to 150 ml, preferably white.
• Three graduated pipettes: one 1-ml, one 5-ml and one 10-ml.
• Graduated cylinder, 50 ml.
• Distilled water.
• Stirring rod.
• 8N NaOH or KOH solution.
• Calcon Indicator or Calver II.
•  Porcelain spoon/spatula.
•  Masking Agent: 1:1:2 mixture volume

• Add 50 cm³ of deionized water to the titration vessel.
• Add 2 cm³ (20 drops) of Versenate Hardness Buffer Solution.
• Add 10 drops of Versenate Hardness Indicator Solution.
• If calcium and/or magnesium is present, the solution will turn wine-red.
• If no hardness is present, the solution will remain blue.
• While stirring, titrate with EDTA (standard Versenate) until the solution changes from wine-red to blue.
• DO NOT exceed the endpoint!
• Add 1 cm³ of filtrate to the deionized water.
• If calcium and/or magnesium is present, the solution will turn wine-red.
• While stirring, titrate drop by drop with EDTA until the color changes from wine-red to blue.
• Record the volume (cm³) of EDTA used and calculate hardness (mg/L) using the formula:

(The value 400 in the equation above corresponds to the use of Standard Versenate 400 solution. If Standard Versenate 4000 solution is employed instead, replace the value 400 with 4000.)

• Add 50 mL of deionized water to the titration vessel.
• Add 1 mL of Calcium Hardness Buffer solution and mix.
• Add 1 mL of 8N NaOH or KOH solution.
• Add ¼ level porcelain spoon (0.2 g) of Calcon Indicator and mix thoroughly using a stirring rod.
• Add a pinch (~0.1 g) of Calver II indicator powder. If calcium ions are present, the solution will develop a wine-red color.
• While stirring, titrate with EDTA (drop by drop) until sample color changes from wine-red to
• blue. DO NOT GO PAST ENDPOINT!
• Introduce 1 mL of filtrate to the solution.
• A wine-red color will reappear if calcium is present.
• While stirring continuously, titrate with 0.01M EDTA solution dropwise until the endpoint is reached (color transitions from wine-red to clear blue).
• Record the volume (cm³) of EDTA used and calculate hardness (mg/L) using the formula:

0.6 in above equation is a ratio Magnesium to Calcium. Since we know that the atomic weight of Calcium is 40.08 and the atomic weight of Mangnesiumis 24.31. (24.31/40.08)=0.606

This involves basic chemistry concepts like molarity, stoichiometry, and unit conversions.
Molarity (M) = Moles of solute per liter of solution.
So 1 mL of EDTA contains:

1 moles of EDTA binds 1 mole of Ca²⁺ (or Mg²⁺),

0.00001 moles of EDTA x 1 mole Ca²⁺ = 0.00001 moles of Ca²⁺

Molar mass of Ca²⁺=40 g/mol

Therefore;

This is 0.4 mg per mL of EDTA.

Total hardness testing assumes you are analyzing 1 liter (1000 mL) of water:

If you use 1 mL of EDTA to titrate all the hardness in 1 liter of water:

This is why 1 mL of 0.01M EDTA corresponds to 400 mg of Ca²⁺