Mixing Half an ORS Sachet in 500mL Water
No, this approach is not recommended—the disadvantage of packets is the potential for mixing with inappropriate volumes of water, resulting in ORS that is either too diluted or too concentrated, which can be dangerous. 1
Why This Method Is Problematic
Measurement Accuracy Issues
Weighing half a sachet introduces significant measurement error. Even trained health professionals struggle with accurate liquid measurement using standard equipment, with errors ranging from -92.0 to 57.5 mL in controlled studies 2. Powder measurement by weight at home is even more prone to error.
The powder components in ORS sachets may not be uniformly distributed. Different ingredients (sodium chloride, trisodium citrate, potassium chloride, and glucose) have different densities and may settle or separate during storage and handling 3. Dividing the sachet by weight does not guarantee you're getting exactly half of each component.
Standard WHO-ORS is designed to be mixed as one complete packet in exactly 1 liter of clean water to achieve specific concentrations: sodium 75 mEq/L, potassium 20 mEq/L, chloride 65 mEq/L, citrate 10 mmol/L, and glucose 75 mmol/L 3.
Serious Risks of Incorrect Mixing
Concentration Errors Can Be Dangerous
Too concentrated solutions (from using too little water) can cause hypernatremia, particularly problematic when solutions exceed 90 mEq/L sodium 1. One study documented hypernatremia development with improperly concentrated ORS 1.
Too diluted solutions (from using too much water) provide inadequate sodium replacement, with concentrations below 30 mEq/L being ineffective for rehydration 4. Field studies have documented sodium concentrations ranging dangerously from 9 to 116 mmol/L when home mixing instructions varied 4.
Gross variations in recommended quantities of sugar, salt and water can result in dangerous or ineffectual concentrations that fail to achieve the critical glucose-sodium cotransport mechanism essential for ORS efficacy 4.
The Correct Approach
Use Standard Mixing Instructions
Always mix one complete ORS packet in exactly 1 liter (1000 mL) of clean drinking water, as this is the only way to ensure correct concentrations 3.
Provide detailed written and oral instructions when packets are dispensed for home mixing to prevent concentration errors 1.
Use the mixed solution within 24 hours if kept at room temperature to prevent bacterial overgrowth 5.
If You Need Smaller Volumes
Purchase premixed commercial ORS solutions (such as Pedialyte or Ricelyte in the United States), which eliminate mixing errors entirely and ensure correct concentration 1. While more expensive, premixed solutions guarantee safety 1.
If you must prepare smaller volumes from packets, use precise volumetric measurement: Mix the full packet in 1 liter, then measure out the exact volume needed (e.g., 500 mL) from the correctly prepared solution. Discard or refrigerate the remainder for use within 24 hours 3, 5.
Critical Pitfalls to Avoid
Never estimate water volumes using household containers without verification—even condensed milk tins used in field studies showed variability, though they performed better than random containers 5.
Do not assume equal distribution of ingredients throughout the sachet—pharmaceutical compounding studies demonstrate that powder uniformity is difficult to achieve even in controlled settings 6.
Do not use this half-sachet method for treating moderate to severe dehydration, where precise sodium concentrations (75-90 mEq/L) are critical for safe and effective rehydration 1.