Preheat oven to 350 degrees. Melt the sugar in a non-stick loaf pan over low heat, sliding the pan around constantly until the sugar is liquid but not burned. Alternatively you could melt the sugar in a separate pot and pour into a loaf pan.
Combine the can of condensed milk, 3/4 of the same can of water, eggs and vanilla extract in a blender and blend until smooth. Pour this mixture over the melted sugar in the loaf pan.
Prepare a bano de maria (bain marie) by placing the loaf pan into a casserole dish and fill the casserole dish with water around the loaf pan until the water is about half-way up the loaf pan.
Place casserole dish with water and loaf pan steady in the middle into the oven on the center rack and bake for about 1 hour. Flan is done when you insert a knife into the center and it comes out clean.
After removing, take the loaf pan out of the hot water and place in refrigerator for 5 hours or overnight until completely cooled. To serve, place a dish over the pan and hold together while flipping upside down. Flan should slide right out once it's cool enough.