Nonsense, water isn't injected to increase the weight. It's done for perfectly acceptable reasons connected with plumpness and moistness and flavour and, most importantly, because the customers like it and demand it. Nothing to do with shamlessley disposing of whey which you'd otherwise have to pay to get rid of elsewhere, coincidentally bulking the meat up shamelessly.
I know this 'cos I've been told it on the radio by various meat industy representatives over the years, so it must be true.