There are different types of polymers that are used in water treatment. They can be stored and transported in different forms.
There is a dry powdered form which is easy and cheap to transport but it is often difficult to mix, requiring special equipment to process it into solution form.
There is a liquid form which is a concentrated solution of a polymer which only requires diluting to use, but it is more difficult and possibly more expensive to transport.
And finally there is an emulsion form which are polymer dissolved in droplets of water in oil. These are not 100% active and can separate out over time which requires occasional mixing. The upside is these can account for various charges in treatment.