Preparation and storage of distilled water

1. Distillation Unit (Water Still)

• • The distillation unit is the main apparatus used for the preparation of distilled water.
  • It includes all essential parts such as the boiler, condenser, receiver, and heating source combined in one setup.

Types of Distillation Units:

• • Single Distillation Unit: Produces water of standard purity suitable for general laboratory use.

  • Double Distillation Unit: Used when ultra-pure water is required for analytical or research purposes.

Construction: Usually made of borosilicate glass or stainless steel for durability and chemical resistance.

Function: To convert impure water into steam and condense it back to liquid distilled water.

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2. Boiler or Boiling Chamber

The boiler (or boiling chamber) is the part of the unit where the actual evaporation takes place.

Features:

• • Holds the raw tap water before distillation.

  • Equipped with a heating coil or burner at the bottom.

  • Made from heat-resistant glass or stainless steel to withstand high temperatures.

  • Includes a safety valve to release excess steam pressure.

Function: Heats water to produce steam while leaving behind impurities such as salts, suspended particles, and organic contaminants.

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3. Heating Element

• • The heating element provides the heat energy needed for the distillation process.
  • Modern units generally use electric heating coils, while older systems may use Bunsen burners or gas flames.

Function: Converts electrical energy into heat to boil water efficiently and consistently.

Note: Automatic thermostatic controls prevent overheating and maintain a constant boiling rate.

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4. Condenser (Cooling Chamber)

The condenser plays a critical role in converting steam back into liquid water through cooling.

Construction:

• • Made up of a coiled glass or metal tube placed within a water jacket.

  • Cooling water continuously flows through the jacket, keeping the temperature low.

  • Cold water enters from the bottom inlet and exits from the top outlet, ensuring maximum cooling efficiency.

Function: As hot steam passes through the coiled tube, it loses heat to the cooling water and condenses into pure liquid water.

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5. Receiver or Collection Flask

The receiver flask collects the condensed distilled water coming out from the condenser.

Features:

• • Made of borosilicate glass or HDPE (high-density polyethylene).

  • Must be clean, sterile, and airtight to prevent contamination.

  • The first 25–50 mL of distillate is usually discarded because it may contain volatile impurities.

Function: Safely collects and stores freshly distilled water immediately after condensation.

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6. Thermometer or Thermostatic Control

A thermometer or automatic thermostat helps monitor and control the temperature of the distillation process.

Function:

• • Ensures water reaches boiling point (around 100°C).

  • Prevents overheating and possible damage to the apparatus.

  • Helps in maintaining consistent operation for uniform steam production.

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7. Cooling Water Inlet and Outlet Tubes

These are rubber or PVC tubes that carry cold water into and out of the condenser.

Function:

• • Maintain a steady cooling effect during condensation.

  • The inlet tube supplies cold water from the bottom, and the outlet tube removes warm water from the top.

  • Some units include flow-control valves to regulate cooling speed and efficiency.

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8. Storage Container

After collection, distilled water must be stored properly to maintain purity.

Requirements:

• • Use clean, airtight containers made of amber-colored glass or high-grade plastic (HDPE or polypropylene).

  • Store away from sunlight, dust, and chemical fumes.

  • Label each container clearly with “Distilled Water – Date of Preparation”.

  • Replace stored water weekly to prevent microbial growth.

  • Avoid metal containers, as distilled water can leach ions from the surface.

Function: Keeps distilled water free from contamination during storage and usage.

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9. Deionizer Unit 

A deionizer unit is sometimes connected either before or after the distillation process to achieve ultra-pure water.

Components:

• • Contains cation and anion exchange resins that remove charged ions (like Na⁺, Ca²⁺, Cl⁻, and SO₄²⁻).

  • Often used in research or clinical laboratories where high-precision tests are performed (e.g., spectrophotometry or chromatography).

Function: Ensures removal of all ionic impurities for the highest grade of purity.

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10. Safety and Supporting Parts

To ensure smooth and safe operation, several accessories are attached to the distillation system.

Common Accessories:

• • Safety valve: Releases extra pressure from the boiling chamber.

  • Drain plug: Allows removal of leftover water and scale deposits.

  • Clamps and stands: Hold the glass apparatus firmly during heating.

  • Rubber stoppers and joints: Prevent vapor leakage.

Function: Prevent accidents, maintain tight connections, and ensure system stability.