testing water for domestic use

hey folks!

i have water harvesting system set up and would like to test the water for quality... no fear of the rain water being undrinkable but the 2 1000 litre tanks could be questionable!

just in the middle of seting up the water pump system.. pics to follow soon

so yea... if some could point me in the right direction.... i have not yet built a slow sand filter... its on the to-do list!