this has been covered many times in the past,anyway pay no attention to anyone who tells you to mix water in to paint for the first coat,or the second coat or any coat,you do not ever put normal white paint on to new solid plastered walls,you need to use acrylic primer for the first coat,and the guy in the paint shop who told you to add water to the first coat is filling you with crap...acrylic primer is what you need stops all the blotches or mapping.acrylic primer is white and thats why people think when they see a new house first coated thats its normal white paint....