Anyone have good experience in flocking using alum?

I bought a spice container of it at the grocery store and did
an experiment with my son. We filled a glass with tap water
and added a spoonful of dirt and gravel. Stirred to get a very
cloudy mix then added a couple of pinches of crushed alum.
Within 5 minutes the water was clear enough to see through again
and a lot of debris was on the bottom.

I am curious about formulas for amounts etc for using this
before treating with other methods. Anyone?

Did you do a control experiment with another glass of tap water and no alum?

Good idea, will try that next.

Did this experiment weekly each summer from 1953-1967: the old man built a 40X15X6 swimming pool in the back yard, and it had no filter. We filled a pillow case with alum and tied a rope on it and dragged it around the pool til gone on friday night, then vacuumed the scum out with a home made pool vac on saturday morning. Sometimes had to add potash to achieve a suitable pH for good flocculation, or something.

But removal of suspended particles does not mean that the water is safe to drink. It only means there is less "crud" in it.

Removal of organics can make sanitizing chemicals more effective, especially for chlorine-related chemicals. I'm not sure if that is the case with iodine.

I suspect that water treatment plants use floculation (real word?) because it is more suited to large volumes of water than filtering - are at least more cost effective.

A reduction in turbidity is usually correlated to a reduction in water-borne pathogens, so in general, we can say that the water is safer than it was before. But not necessarily safe to drink.

Neat. Thanks for the post. Seems like a decent pretreatment process if nothing else. How did your control experiment turn out?