i'm sure you already know this, but on the off chance you don't.
do NOT trust your tap water will be constant.
you may test it a couple times and it is the same, so you assume it will but that isn't the case.
e.g. i'm on city water, they use multiple wells, the yearly report shows a "average" number, and then a range.
recently when trying to figure out if some sand i used was changing my pH, i noticed the tap pH changed from 8.4 to 7.4 over a couple days.
do NOT trust your tap water will be constant.
you may test it a couple times and it is the same, so you assume it will but that isn't the case.
e.g. i'm on city water, they use multiple wells, the yearly report shows a "average" number, and then a range.
recently when trying to figure out if some sand i used was changing my pH, i noticed the tap pH changed from 8.4 to 7.4 over a couple days.