Language is ambiguous and answer can be C or E based on how it is interpreted
Let Capacity of water in kL be W
Statement 1
Let current capacity be x
x+430 = W
Since we don't know x, we cannot find W
Insufficient
Statement 2
Reservoir is normally filled to 65% doesn't tell me W
Insufficient
Combined, I don't know what x is. Cases:
1. If we assume x is normal capacity of 65%, then answer will be C, as the capacity W can be found using 35% of W = 430. On exam I would go with C though, as I believe GMAT won't trick on Quant DS like this
2. If we assume x is still unknown, because we don't know if x is normal capacity or some water has been taken out of it. Then answer is E, because we still don't know x to solve for W
Bunuel
How many kiloliters of water are in a reservoir?
(1) If the reservoir were filled to capacity, there would be 430 more kiloliters in the reservoir.
(2) The reservoir is normally 65 percent full.