The only time it's acceptable to mix water in the paint is when you're using a deep or ultra deep base paint to reduce its stickiness, which is rare with new paint technology. Dark primary colors are composed almost entirely of tint that makes it very hard to work with without adding water. (You never use a sprayer and need to thin paint.?) If i was still in the industry I'd take the time to make a better article than this. Take this for a grain of slat. Use a reputable painter or someone you know you can trust or has been referred to you by someone you trust. I wouldn't hire anyone I had to watch like a hawk to make sure they're not screwing me.
Taking a few moments to read the following few pages could save you both money and frustration by avoiding a bad contracting experience.  The fact is, painters range in the quality of services they provide, and there are many inexperienced, unlicensed and unqualified people and companies that masquerade as professional painters. Many homeowners are so focused on “how much” that they never even consider anything else. This can lead them to hire the wrong company.
Paint gets more expensive as you go from flat to gloss. The difference is usually around $1 per gallon per sheen upgrade. Flat is the cheapest, then matte flat or eggshell, satin, semigloss then gloss. Paint also gets much more expensive the darker it gets. A white or neutral paint color can be as much as $20 less expensive than a deep base red or blue.
This is an area that interior painters can easily cut short to save time. Most contracts don't state the extent of the wall repairs included, so it's up to the painter's discretion how much they will do. If it seems like too much work, they'll usually point out the repairs but don't include it in the bid. They'll then ask you if you'd like it fixed after they start your project and let you know how much more it will cost. House Painting Parker Colorado