People are going to give you broadly different answers about what paint they like. After GW discontinued every color in my palette (in some cases more than once) I vowed to never buy another GW paint pot again, though some people really like them.
Lots of people love Vallejo, though I dislike the dropper bottles and am often less than thrilled with the consistency. However, Vallejo is readily available, and is good for matching old GW colors, and they've never discontinued anything.
I prefer the P3 paints, though they are a little more expensive, and less available (I have to order mine online, which is inconvenient). I think they have superior consistency and opacity. They are also sold in pop top pots similar to the very old (ten years or more now) GW ones, which don't dry out. The droppers don't dry out either, but you also can't easily scrape the bottom of the pot.
I don't think adding water to paint is an inconvenience; it is exercising control over the paint's consistency. I also use a wet palette, which automatically adds water, but that might be beyond the scope of this discussion.
I keep two things on hand to add to paint in addition to water. The first is acrylic medium. The only hobby line to sell this that I know of is P3 (and I've never used theirs), but it's readily available in the acrylics section of your local art supply store. Acrylic mediums come in a range of viscosities and finishes, so make sure you're not getting one that's too thick (it will say if it is, if it just says something like "matte medium" it'll be fine). I like Golden, but Winsor & Newton or whoever will be fine.
Basically, this stuff is acrylic paint without the pigment. It's good for resuscitating old paint that's starting to dry out. It's good for making paint more workable without making it runny. I use it a lot for glazing, when I want very translucent paint but I don't want a very thin consistency.
The other stuff I use is called retarder (again, I use Golden's), and it slows down the drying time of acrylic paint. I use it when my wet palette is being finicky but adding water would flood the paint I'm working with, and when I'm doing fine detail freehand work and don't want the very small quantity of paint on my very small brush to dry there instead of on the model. If you get retarder, use it sparingly, because if you add too much the paint won't dry properly. Also, retarder can reactivate dried paint, so be careful you're not contaminating the color on your palette with something previously dry underneath.
When one of my paints starts to dry out I add water, medium, and retarder until it becomes cooperative again.
I don't know if your paints are drying out or just really separated or both (that can happen sometimes). Hopefully something in this ramble is helpful for you.
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