Although you can use water as a solvent for acrylics I am still convinced that the correct manufacturers thinner gives better results. One of the biggest concerns is when spraying. If the thinners does not evaporate at the same rate as the paint then you could get a poor surface due to the viscosity of the paint varying. Manufacturers thinners is designed to evaporate at the same rate as the paint so the viscosity remains constant through out the drying process.
Also you only have to try to clean you brush in water and then in the correct thinners to see how more effective a solvent it is. The temptation of course is that water costs you nothing but what is the cost to you of an imperfect finish with visible blemishes or particles?
I always use the relevent manufacturers thinners. Tamiya acrylic thinners is a world apart from using water and well worth the expense.
I don't think there is any conflicting information on this, water can be used but proper thinners is better at the job.
As Dicky says, and I always tell people the same, experiment with paints, do sample pieces so that you are sure what to expect when you apply the paint to the actual model.