All right party people, here's the deal:

You can't determine presence/absence of chlorine by testing pH.

MArijuana likes a pH that is slightly acid, approximately 6.3 to 6.8.

Did you know that distilled water, when allowed to air-equilibrate, actually has a weakly-acid pH as a result of atmospheric CO2 going into solution and going into equilibrium with Carbonic acid?

Lake and rain water will 99% of the time be slightly acid as well.

LAke water does contain low levels of dissolved nutrients; the amount varies depending on the region, the watershed, the substrate, biological activity, time of year, etc.

If you use tap water and really worry about chlorine, you can let it sit with an airstone in it overnight to air-equilibrate. At room temperature, pure Chlorine exists as a gas. In natural lake water, it will be found as an part of a molecular substance such as sodium chloride (NaCl) which is table salt, or CaCl, which is road salt, or any of an innumerable array of substances.

The amount of chlorine left in tap water after leaving it out all night should NOT harm you plants.

If you want to test for chlorine, pool supply stores should have chlorine test kits in stock, but the sensitivity is low because of the very high levels of Cl expected in swimming pools.