Hi F - have to add a comment if only to gain another bobble for my hat - supermarkets are factory outlets - it so happens that the product they flog is food, not sofas or whatever.
If there is a bargain to be had, ask why, how, to whos benefit and similar queries before giving over your money which no doubt you work darn hard for.
Food is all most people eat, so why is the appeal of saving �2 such a draw?
If you bought the quality of, say chicken, from a reputable butchers, farm shop or farmers' market producer who can give you the provenance of the item, advise the best way to prepare and cook, etc, then as noted above from N/flakes comment, the difference in the texture, density of flesh, flavour of the bird and so on will really make you think about what you by from s/markets.
Loss leaders like this are there to get shoppers into the habit of spending in 1 store, not to offer great tasting products at bargain prices.
Food is too important to waste money on - DEFRA recently suggested 20% of what is bought in s/markets is thrown away - thats the same as �450 a year in the bucket....
And yes water is added, and for different reasons - Tescos Finest Pork fillets? - 87% meat - the rest is water....It is a cheap ingredient and bulks up products, especially frozen ones. The Dutch food industry are the masters at creating 'added benefits' for processed goods - beef DNA added to chicked 'cos it holds more water when frozen is 1 example....
Read the labels on goods, meal plan, buy what is in season, and patronise the local outlets - you will not be disapointed and will get flavoursome food and save money too......