Sautee the onion with half the oil. Add the rice and let cook for a few minutes. Add the dill, the hot water and salt and pepper. Boil for about 5 minutes. Let it cool.
Steam the grape leaves and rinse with plenty of water in a collander.
Wrap the rice mixture with the grape leaves. This is the most difficult and time consuming part, although after you are through it a couple of times you enjoy it the most. It is better if two people work on it simultaneously, talking, joking etc. You want to make them small in size (about 1-2 inches.) Do not hesitate to cut big leaves in half. Discard the central stem of these leaves and if you can reduce (with a sharp knife) any other tough stems it would be good. You want to wrap the rice very tightly. You place the rice in one end, fold from the short end and the two sides and then roll while pushing the rice downwards to pack it really tight. You have to do it a couple of times to understand. If they are not tightly packed they will unroll later. Also be careful to wrap totally, do not leave any holes.
You arrange the dolmadakia in a casserole, tightly. Make more than one layers. Add the lemon juice, the rest of the olive oil and 1 1/2 cups of hot water. Cover them with a plate or something to keep them in place. Let them simmer for 35 minutes.
Serve then cold, with strained yogurt or taramosalata. Enjoy.