I was taught to paint by a professional and when estimating the amount of paint needed, I always allow for a second coat just to make sure of coverage. We interviewed a painter who tried to tell me I bought poor quality paint without knowing where I purchased it, and stated he would have to buy all new paint. He had not seen the cans and was just guessing so I asked him where I should buy paint from now on. It was the same place I had purchased my paint and he wanted to charge me an extra 20 a gallon more than what I paid for. Needless to say, I have interviewed numerous painters and they are not all honest.
Never, never hire "Hanks painting" , he is a scam. He charged me 1800 for an 800 sqft house, with the agreement of painting the gutters. He not only didn't paint the gutters, the paint of the walls and front door is pealing off. He did not sand the door and the wall color is washing off. His people don't know the work and he much less than them since he painted the door.
Back to the article. You can add water to all latex based paints / thinner to oil based paint. The tinting base has absolutely nothing to do with it. Say you are working outside and throughout the day you have to add a little water to keep the same consistency. If somebody really tried to add 20% to 50% water they no longer would be painting they'd be performing a whitewash or pickle finish.