Aquatabs contain NaDCC (sodium dichloroisocyanurate) as the active ingredient. When dissolved in water, they release free chlorine (HOCl / OCl-) for disinfection. Commonly used for drinking water purification and emergency water treatment.

Low-dose Aquatabs (e.g., 1.67 mg) are ideal for small volumes. One 1.67 mg tablet in 1.5 L of water gives approximately 1.1 ppm, which falls within the recommended safe range of 0.5–5 ppm for drinking water during camping or trekking. If 1.67 mg tablets are not available, half of a 3.5 mg tablet can be used as an alternative.

However, in some areas only high-dose tablets (e.g., 500 mg, typically meant for 150 L water tanks) are available. In such cases, direct use is not practical for small volumes.


Safety Note:

Do not directly estimate or fraction high-dose tablets in the field. Prepare a high-strength stock solution, then use a small measured amount from it to treat drinking water to ~1 ppm.


Stock Solution:

A small ~500 mL 7up bottle works well for the stock solution. Its dark green color helps reduce light exposure (protecting chlorine), and keeping it in a backpack further limits sunlight and heat. The tight cap also helps minimize chlorine loss due to gassing. Below is a simple method to do this:

1 ppm = 1 mg/L (for water)


Typical composition of Aquatabs (NaDCC formulation) as per Medentech (manufacturer) literature is:


This means the labeled tablet mass is not entirely available chlorine. Available chlorine will be 60% of 500 mg (theoretical maximum).


500 mg × 0.60 = 300 mg, So:


Therefore stock solution = 600 ppm



1PPM Solution


Next step is to calculate how many mg you need to make 1 ppm in 1.5L. A typical Nestle drinking water bottle is 1.5L that's why considering this 1.5L value. 

If 1mg in 1L is 1ppm and 2mg in 2L is 1 ppm then 1.5mg in 1.5L is also 1ppm. Mathematically: 


So you need 1.5mg from your stock solution to transfer it to your 1.5L bottle to make it 1ppm. Since stock solution is in ml, next step is to calculate how many ml will 1.5mg be? 


Our stock solution had 300mg in 500ml. Mathematically: 


So taking 2.5ml from stock solution and transferring it into 1.5L water bottle will make the drinking water 1ppm in strength.


 

Dosage

Use a small syringe to draw 2.5 mL from the stock solution. It’s lightweight, easy to carry, and allows precise measurement.

Note: 1 ppm of chlorine from Aquatabs (NaDCC) is generally not enough for safe drinking water in a camping or backcountry setting. While 1 ppm is a standard target for municipal tap water, it is insufficient for "raw" or "wild" water because it does not provide a high enough concentration to reliably kill resistant parasites like Giardia in a short period.




Experimental Testing:

Based on the above preparation, it was calculated that 2.5 mL of stock solution in 1.5 L water would produce 1 ppm free chlorine. To check this, free chlorine was measured using a high-quality Taylor test kit.

However, actual testing showed deviation from the theoretical value i.e. 4 mL of stock solution in 1.5 L produced ~1 ppm, rather than the calculated 2.5 mL which produced less than 1 ppm.


This indicates that the effective free chlorine availability in the prepared stock solution is lower than theoretical assumptions, likely due to:



Stability Observation:


The same 1.5 L prepared solution was retested after 7 days:



This suggests that the effective strength of the stock solution decreased by approximately 50% over one week.



Conclusion


Theoretical calculation (based on 60% available chlorine):


Experimental result:


This suggests that the effective working concentration of the stock solution is closer to ~375 ppm, corresponding to approximately 188 mg of active chlorine (38% of 500 mg, not 60%) in 500 mL, instead of the theoretical 600 ppm. The discrepancy arises from the difference between theoretical available chlorine (manufacturer specification) vs measured free chlorine under real-world conditions. Despite this variation, the method remains: