This processing drinking water.
The water comes in and the particulates within it carry a negative ion charge. The water passes over an agitator, and a combination of ferric chloride and some kind latex are mixed with the water.
The water then flows through a long channel. At this point the negative charged particles bind with the positive charged chemicals. The combinations then simply precipitate out in the long channel. At the end, small channels draw water off just the first few inches of the larger channel.
This water goes to a combination aggregate and sand filter. It’s not very deep, about 3 feet total for both.
The resulting water is 99+% pure now.
It moves on to a large activated carbon filter. We’re talking 10 feet deep. Like a water pitcher filter. This is a recent CA requirement, installed in 2005. Designed to remove some specific by products.
The water then goes through a large UV system to kill what’s left, and is finally injected with some chlorine. The chlorine is preventative to deal with anything that may potentially be introduced later in the system.
I don’t know when they intrythe UV part, but the way it’s laid out, seems like that came with the carbon filter system.
That means that prior to 2005, the aggregate and sand filter was considered good enough, augmented with the chlorine. But they never considered the chlorine as part of the purifying process, simply precautionary.
It was very interesting, and I thought pretty simple conceptually. The trick is the actual engineering of the actual plant and respective water system.
I found it interesting to learn that the large water tank near me, which roughly measured at 5M gallons is actually only 1/3rd above ground. It’s a 16M tank, one of the largest in the system.