Citigroup upgraded Pentair (NYSE:PNR) to buy from neutral and increased its target price on the company to $45 from $39 after the company announced the acquisition of the privately held water filtration company Norit for $705 million.Norit CPT, based in the Netherlands, is a global leader in water filtration, which the bank considers the sweet spot of the water industry. The transaction is immediately accretive, without any heroic assumptions on synergies, Citigroup noted.Pentair has a potential upside of 6.9% based on a current price of $38.5 and an average consensus analyst price target of $41.14.