Lipids are insoluble in water because lipid molecules are : -

Lipids are mostly made of long non-polar hydrocarbon chains (fatty acids) that cannot form hydrogen bonds with water.
Such water-repelling molecules are called hydrophobic; they dissolve in non-polar (organic) solvents such as chloroform, ether and benzene, but not in water.
So lipids are insoluble in water because they are hydrophobic.