The invention provide a class of water-processable polymerizable prepolymers which comprises (1) siloxane-containing monomeric units derived at least one siloxane containing monomer having one hydrophilic group or chain and/or polysiloxane-containing crosslinking units derived from at least one hydrophilized polysiloxane or chain-extended polysiloxane crosslinker; (2) hydrophilic monomeric units derived from one or more hydrophilic vinylic monomers; and (3) from about 0.05% to about 5% by weight of polymerizable units each having a pendant or terminal, ethylenically-unsaturated group and free of any polysiloxane segment. The prepolymer comprises from about 20% to about 50% by weight of silicone relative to the total weight of the prepolymer and has a high water solubility or dispersibility of at least about 5% by weight in water and suitable for making silicone hydrogel contact lenses.