BIS standards for water limits Nitrate in drinking water to 40 mg / l, or 40 ppm.
 
The ffem Nitrate test kit provides you with a means of monitoring water for Nitrate rapidly. The test used is a colorimetric test using a two powder reagent supplied in sachets. The reagent induces a colour change in the sample depending on the concentration of Nitrate 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 Nitrate in drinking water, please have water sample tested at certified laboratories while deciding on the fitness of a water source for drinking purposes.