Shares in Northumbrian Water gushed higher after Hong Kong Infrastructure group Cheung Kong (CKI) said it was sizing up an offer for the water and waste management group."CKI is in the preliminary stages of assessing a potential cash offer for Northumbrian Water," the company said. "There can be no certainty that an offer will ultimately be forthcoming."Cheung Kong invests in energy, transport and water infrastructure in Hong Kong and mainland China and internationally. Its UK investments include Southern Water and Cambridge Water.Northumbrian Water operates in the northeast of England.---RG