regular tap water contains small % D2O , let say a distillation process remove small amount of H2O . how can one measure this change using tools available to average person.
Apart from $D_2O$ (heavy water), natural water also contains $HDO$ (semi-heavy water) and of course $H_2O$.
The physical properties of these substances do vary from one to another, as can be seen from this Wikipedia comparative table. For example, the melting point of $D_2O$ differs sufficiently from that of $HHO$ or $H_2O$ to be measurable by a hobbyist or amateur scientist.
The problem is that deuterium ($D$) has very low natural abundance: only 1 in 6420 hydrogen atoms is deuterium (in the world's oceans), according to Wikipedia.
At such low abundance of $D_2O$ and $HHO$ the influence of these substances on the bulk properties of tap water is beyond reasonable means of measurement by an "average person". And a single electrolysis has only a small effect on these low abundances.
The same is true on the effect such low abundances (and any small changes thereof) on biological systems, even though much higher concentrations of $D$ does have a strong negative effect on the metabolism of most animals (like fish).
In "ordinary" water, about 156 out of 1,000,000 hydrogen atoms are deuterium.
If you were to pick any instant in time, these atoms would be arranged in water molecules as follows:$$HHO---0.999688024$$ $$HDO---0.000311951$$ $$DDO---0.000000024$$ So only about 24 molecules of true heavy water exist in a billion molecules of ordinary water.
In addition, these hydrogen and deuterium atoms are rapidly exchanged in water. If you were to watch a particular one of the tiny number of $D_2O$ molecules, (don't ask me how) you would see the D atoms swapped out (and possibly back in again) very quickly.
I don't know any "kitchen-sink" method to detect the effect of removing a few of the super abundant H atoms...