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...