The following compilation is a combination of our own findings and the information provided from the Berkey Knowledge Base.

Oxidation-reduction potential, or ORP, is a measurement that indicates the degree to which a substance is capable of oxidizing or reducing another substance.ORP is measured in millivolts (mv) using an ORP meter. A positive ORP reading indicates that a substance is an oxidizing agent.

It is our findings that the Black Berkey® Purification Elements reduced our tap water ORP here in Melbourne by an amazing 40% also with a slight increase in PH, this is of course not an official certified laboratory test but the findings of a reliable calibrated water test equipment and for those studied in water filtration this shows that the ORP of water treated by Black Berkey® Purification Elements  and process medium of the 6 proprietary blend would observe this as an indication of such a drop below that at which the oxidants like chlorine and chloramine and other organic contaminants are not stable in a reduced oxygen environment.

Also from a physical observation findings, the top reservoir of our Royal Berkey reveals the overwhelming smell of chloramines and a host of other contaminants we are grateful to now not have circulating in our body. We ourselves are adamant practicing raw plant based consumers (aka vegan) appreciating the natural taste and nutritional benefits of our Berkey®

The Berkey knowledge base reveals

What is ORP?
ORP stands for Oxidation Reduction Potential or Redox. It is the activity or strength of
oxidizers and reducers in relation to their concentration in water. It is not (like pH) a
measurement of concentration, rather of activity level. Different meters are available to
measure the ORP in your water. ORP is measured in millivolts (mV) with no correction
for temperature.
In theory, the higher the ORP reading, the less potential for bacterial activity in the
water, and vice versa. ORP measurements are typically taken for drinking water, spas,
swimming pools, etc.
The ORP measurement went down after running my water through a Berkey®
system. Is this OK?
Actually, yes. The Black Berkey® purification elements at the heart of your Berkey®
system are capable of reducing a whole host of potential contaminants from your water,
starting with viruses and bacteria. In that these possible contaminants are already
removed from your purified water, the ORP measurement becomes irrelevant as
disinfection is no longer necessary in your post filtered water. While a higher ORP
would be desired for untreated water…this is simply not the case for water purified using
a Berkey® system.
Further, using meters available to measure ORP is not a perfect science. For example,
“…ORP relationships are not uniform for all oxidizing disinfectants…research has
shown that ORP is not a practical method for monitoring the antimicrobial potential of
water treated with hydrogen peroxide or peroxyacetic acid.” (1)
(1) If you would like to read more information on ORP, reference this document from the
University of California: http://anrcatalog.ucdavis.edu/pdf/8149.pdf  

Plus also PH question answered via Berkey Knowledge Base

Why is my PH level higher after using the Black Berkey® Purification Elements?

When water is filtered through our system, the Black Berkey® Purification Elements increase the PH level of the water. This is healthful because pathogenic bacteria and viruses thrive in acidic environments and have difficulty surviving in alkaline environments. An environment with more alkalinity does have a higher PH level. The PH level will depend on various factors including what the PH level of the pre-filtered water is.