For the OP, some additional information. 
Casual water, as well as Ground Under Repair, fall under Abnormal Ground Conditions. The committe ruled correctly because you can not drop outside a bunker due to an AGC without penalty. Reason being the bunker does not lose it's status as a hazard, even when full of casual water.
The issue with all this is changing the status of the bunker from hazard to "though the green" and how to do it.
Decision 25/13 does say if a bunker is deemed to be total GUR, do to renovation, it loses it's status as a hazard, but the rules treat casual water differently.
25/13
Bunker Totally Under Repair
If a bunker is being renovated and the Committee defines the entire bunker as ground under repair, the bunker loses its status as a hazard and is automatically classified as "through the green." Therefore, unless a Committee specifically states otherwise, Rule 25-1b(i) applies, not Rule 25-1b(ii).
What the committee needed to do is spelled out in Decision 33-8/27.
33-8/27
Local Rule Providing Relief Without Penalty from Bunker Filled with Casual Water
Q.May a Committee make a Local Rule allowing a player to drop out of any bunker filled with casual water, without penalty, contrary to Rule 25-1b(ii)?
A.No. The Committee may not make a Local Rule providing generally that flooded bunkers are ground under repair through the green, as such a Local Rule waives a penalty imposed by the Rules of Golf, contrary to Rule 33-8b.
However, in exceptional circumstances, where certain specific bunkers are completely flooded and there is no reasonable likelihood of the bunkers drying up during the round, the Committee may introduce a Local Rule providing relief without penalty from specific bunkers. Prior to introducing such a Local Rule, the Committee must be convinced that such exceptional circumstances exist and that providing relief without penalty from specific bunkers is more appropriate than simply applying Rule 25-1b(ii). If the Committee elects to introduce a Local Rule, the following wording is suggested:
"The flooded bunker on [insert location of bunker; e.g., left of 5th green] is ground under repair. If a player's ball lies in that bunker or if that bunker interferes with the player's stance or the area of his intended swing and the player wishes to take relief, he must take relief outside the bunker, without penalty, in accordance with Rule 25-1b(i). All other bunkers on the course, regardless of whether they contain water, maintain their status as hazards and the Rules apply accordingly."
In a competition played over more than one round, such a Local Rule may be introduced or rescinded between round.
In my opinion you got a raw deal. The ruling was correct, however IMHO the committee did not properly do it's job. It sounds like the bunker was flooded before the round started and as such the local rule should have been in effect.