To calculate the electric field generated by a charge above a water-filled container, it's essential to consider the different electrostatic constants for air and water. The method of images is commonly referenced in textbooks for such scenarios, treating the water surface as an infinite plane. However, some participants question whether this method is applicable since it typically assumes a grounded perfect conductor. An alternative approach using Gauss' Law and Cartesian coordinates may also be viable, though it requires careful trigonometric adjustments for the water's surface. Overall, both methods have their merits depending on the specific conditions of the problem.