What is meant by the term osmoregulation ? What are the problems faced by osmoregulators?

Osmoregulation is a process that regulates the body’s salt and water concentration.
Osmoregulators face some problems :
(a)In hypotonic medium, endosmosis occurs, therefore osmoregulators must eliminate excess water.
(b)In hypertonic medium, exosmosis takes place, hence they must continuously take water. These also have to spend energy to move water in or out.