Change in colour of water to yellow from bore well in Kottayam, Kerala - Need the reason and solution to the problem

sir,

   The colour of water from my tube well changes to yellow after some time.It clear when it is pumbed into the tank,

but aftr a day,the colour chnges to yellow and also there is a yellowish ptt.The same problem is there in near by tube wells.

What could be the reason and is there any problem in using this water.Can anything be done to purify the water.