Also prime the ends of adjoining boards. This step pays off by slowing the moisture penetration that can lead to peeling at the joints. If the new siding is redwood or cedar, buy a special “stainblocking” primer. Both of these woods contain natural chemicals (tannins) that can bleed through paint, causing brownish stains. A stain-blocking primer will seal in the tannins.
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.