The batter should not be too thin, or else it will not coat the vegetables well. So, go easy with the water. If you feel the batter is too thick, you can always add more water. Remember the batter tends to get thin if you let it sit long!
We have determined the nutritional value of oil for frying based on a retention value of 10% after cooking. Amount will vary depending on cooking time and temperature, ingredient density, and specific type of oil used.