"What is the chlorine residual at your household tap?"
The answer may depend upon who is doing the sampling - and what answer they would prefer to see.
Any value from zero residual at the 'first draw' for your morning coffee to the distribution main's total residual can be recorded, depending on the volume of water drawn before sampling. Where household plumbing is flushed for three to five minutes before sampling, as recommended by the AWWA Committee on Bacteriological Sampling Frequency in Distribution Systems (1985), it is the distribution system main, and not the consumer's tap, which is being sampled.
Part of the reason your system might be purged before sampling is that it is always summer for your heated household plumbing. Warm temperatures encourage microbial growth, nitrification, oxygen depletion, chlorine depletion and, sometimes, corrosion of plumbing materials.
To purge microbial growth and their by-products, one is well-advised to run the water until it is as cool as the water in your water distribution main.
For the few that are interested in this microbially-mediated phenomena, the attached paper may explain why.