I can see why you can't order too much water for delivery, it's cheap and heavy and is a lot of trouble to transport and deliver for the profit made.
In my local tescos yesterday there was a sign - yes there was! - saying that they would only sell 4 portions of anchor butter per person.
I asked why, out of interest. The checkout lady said that anchor was half price and that shopkeepers would buy them to sell on in their shops at full price, and then there would be none left for other buyers.
I understood it perfectly, but at the same time felt that if they don't want people will buy their products for such a purpose then they shouldn't sell them at such a low price? Goods for sale, someone wants to buy them, has the money, so what? If Tesco are selling a product cheaper to the general public than a small shopkeeper can buy that product from the wholesalers, isn't something wrong?
I went on about it so much that she regarded me with deep suspicion and said "Do you own a shop" in a tone that suggested she had put security on alert.
After all, butter is butter. And if there is no anchor you'd just get another brand, wouldn't you?
As for the shelves being empty, that often happens anyway when there is a special offer, even 20p off. Surely one person buying twelve of something is no more inconvenient than twelve people buying something they don't usually buy because it is being promoted.