In a blender or mixer add water, butter, sugar and milk powder.
First put it on low speed for a minute till mixture becomes homogeneous.
After few minutes increase the speed and mix till everything mingles together and mixture becomes smooth and creamy. It may take 3-4 minutes.
In between scrape the sides of the jar couple of times so that everything mixes together.
Once the condensed milk is ready you can store it in glass bottle or airtight container and keep in the fridge for multiple days.