BIS standards for water limits Residual Chlorine or Free Chlorine in drinking water to between  0.2 mg / l, or 0.3 ppm, to 0.8 mg / l or 0.8 ppm.
 
The ffem Residual Chlorine test kit provides you with a means of monitoring water for Chlorine rapidly. The test used is a colorimetric test using a  liquid reagent. The reagents induces a colour change in the sample depending on the concentration of Chlorine present. 
 
You can get fairly accurate readings of this colour change using the ffem match Android app. You will need to calibrate your Android phone first, and calibration standards are provided with the kit. Alternatively you can read semi-quantitative results using the colour card provided using your visual judgement, or using the app.
 
Since the kit contains chemical reagents, they are shipped by road, delivery could take between 15 and 30 days depending on the destination.
 
You will also need distilled water (not supplied with the kit) to dilute samples and to calibrate phones.
 
Disclaimer: While the reagent and the app are a fairly accurate way of estimating Residual Chlorine in drinking water, please have water sample tested at certified laboratories while deciding on the fitness of a water source for drinking purposes.