REALITY - This rule is not carefully enforced. Here are some clues in case you're skeptical...
Location of bag screening station - The bag screening stations are located just BEFORE you enter the area with the ticket booths AND the lockers. Disneyland rules state you can use the lockers for food. If they were serious about this, wouldn't they locate the lockers before the screening? So if the screener notices food or drink in your bag, just say you'll put it in the lockers.
Non-Disney Food and Drink is Everywhere - As you enter the parks (Disneyland or Disney California), you'll see many people with non-Disney food and drink. People with strollers have the most freedom (babies and tots have "specific dietary restrictions"), you'll see just about any food or drink possible inside the gates.
Clearly the screening for food and drink is pretty darn porous.
SUMMARY - As long as you are not obvious (don't bring in coolers) and camouflage your water and food in your bag, it's very unlikely the screeners or any other Disney employee will balk. If they do, say you'll put in in the lockers.
I just hope they're more diligent about the items that really matter, like knives and guns :)
|The Unofficial Guide to Disneyland 2007 by Bob Sehlinger|
|101 Things You Never Knew About Disneyland: An Unauthorized Look At The Little Touches And Inside Jokes|