The answer to this question is low density as Gases in general have low densities as their particles are very far apart. Their inter-molecular spaces are actually large. And The number of molecules per unit volume in a gas are small when we put them in comparisons with solids and liquids. That is why they have low densities.
Filtration is useful for separating sediments that are carried in water for easy drinking without the risk of disease - an example of this is a water purifier
