I'm an environmental engineer with some experience in drinking water treatment.

I doubt it's in the drinking water. One of the oldest drinking water treatment methods would remove the virus: slow-sand filtration. Most places in China would at least use this, and South Korea is likely using more advanced technology.

Is the reason sand filtration effective, because the virus is too big to fit between the sand particles as the water flows around it?

I have no clue on how it works, so any insight is appreciated.

The virus particles would be filtered out at the top layer of the sand filter, where a layer of microbes grow. This layer is referred to as the schmutzdecke. https://en.wikipedia.org/wiki/Schmutzdecke

Most of the filtering action happens in that layer. Viruses have no problem getting past sand particles.

Thank you for that info.

I also found this report, which may be of interest, from the University of Arizona in 2008 for Coronavirus survival in water and wastewater:

https://west.arizona.edu/sites/default/files/data/Gundy2008_...

10 days or more in water, and 2 to 4 days in wastewater.

My local municipality only uses chlorine, so I am a bit concerned.

We had our own sand filtration system, but ‘decided’ to instead use the town next-door’s system, instead.

I understand that is an older method, but I would be surprised if it is the method of choice for these cities.

What do you consider ‘advanced technology’?

I studied drinking water treatment in school and worked on a treatment plant design in Ecuador, so I do not have professional experience inside the current modern industry. But as far as I know slow-sand filtration and it's variants are still commonly used. Most of the improvements come from additional processes.

Improvements on slow-sand filtration are from additional pre-treatment methods, disinfection, more advanced filtration media like activated charcoal, and additional stages of filtration using a variety of media. Some high tech treatment plants are using biological membranes for wastewater-to-drinking-water treatment, but that's quite rare as far as I know.

Here's a decent primer of the commonly used processes: https://www.cdc.gov/healthywater/drinking/public/water_treat...

Chlorine. They put it in water for a reason.

I upvoted you...

Right, but Chlorine is only effective against certain types of virii.

Some municipalities instead use some sort of chloramine, or both.

In, addition, neither of these is effective on some virii, so UV is used also.

I am no expert, but from what I have read so far, depending on the virus, the above solutions differ in effectiveness.