Maybe so. I used to work for a company that designed systems of this sort. It was interesting to see how they did what they did. I wasn't an engineer, so my understanding of it was limited- but it seemed to be a highly sophisticated process.
Actually I am an industrial water treatment technician. So I can say with a little confidence that their water treatment systems will more than likely remove the Polonium. All of my following comments are from general knowledge as I am not specifically familiar with Polonium. It is not a common contaminant in water.
If they use an Iron Salt in their Coagulator it may remove it as most heavy metals are attracted to iron.
Ion exchange may also remove Polonium. Especially if the Ion exchange bed is new.
Activated carbon may also remove the Polonium. Many impurities that are not removed by ion exchange would be removed by carbon.
The addition of Chlorine and ozone are not likely to be helpful as they are typically added at the end of the treatment process. A remote possibility is that the Polonium might react with the chlorine and become more chemically reactive with iron and bond with the iron water pipes long enough to decay to a non-radioactive isotope.
Justa-hairyape’s comment;
I have seen the following statement somewhere in the past. 'Dilution is the Solution'. Do not remember where I saw it though. Perhaps someones trademark ?
Is a sarcastic slogan made up by the Environmental and anti-nuke activist back in their haydays of the 70’s. It referred to Nuclear Power Plants discharging radioactive contaminated water to the environment. In the early days of Nuke Power dilution was the primary means of making waste less harmful.
Actually dilution in this case is probably going to be the primary means of rendering the material safe. London’s treated waste water is probably discharged in to the Thames and London being not far from the mouth of the Thames it is unlikely that there are intakes for drinking water lower on the Thames than London’s discharge before the Thames dumps in to the Atlantic. With Polonium 210’s half life of 138 days and dilution of un-told trillions to one I would doubt any trace of it would be found in the water treatment plant in a year (if you could find it now).