Soil run off test ?

Can someone please explain soil run off test to me. If I understand this some what you moisten the soil wait a bit then water with a neutral ph 7 collect the run off and test ? So what if you always water with a ph of 6.5 and your run off is lets say 5.5 and you flush every two weeks. Are you to raise the ph of your water that you give them ?

So does this mean I am the only one who uses soil indoor ? I am thinking not!