Importance of Water Content in Butter?.

This is terrible news but don't despair. You just need to use the right fail safe butter. American supermarket butter is high in water content. European butter low. You want the low water content so try a European butter. Butter is never 100%fat, there is always water called buttermilk, residue from separating the fat (solids) from the water (milk) to make butter and solids like protein.
To make beurre noisette for your recipe the moisture has to be cooked enough so the solids brown, it's best to start with a quality high fat butter. It sounds like some of your butters are just too high in moisture. Choose a natural yellow butter for more colour, these will also be European as they make butter from pasture fed cows. Corn fed, like in America, produces white butter that is sometimes dyed yellow or indeed even the cows are fed things not normaly in a cows diet to change the colour. Read the ingredients anyway it should just say butter but this sadly depends on your labelling laws again. Pasture fed European butter is high in carotenes and unsaturated fat giving it that rich yellow colour.
European butters have to be by law min 82% fat to be sold as butter but between 82% and 90% is normal and will be labelled as such. In America its only 80%. More water more profits as pressing water out the fat lessens the volume. I find it incredible that some butters are so high in water in America that they don't brown, these butters will in effect stew when melted and are not good for anything other than eating as is. Though even here European butter is healthier.
There are a few American "artisan" butters produced from pasture fed and with low moisture content but generally maybe not easily available so you cant fail by just choosing a European one commonly sold in the US like the Irish "Kerrigold". New Zealand also has the same high food standards as Europe so "Anchor" I think its called is a safe bet, as well as more easily found Scandinavian "Lurpack".
American butter is as much as 16 - 18% water and 2 % solids other than fat.
Those seemingly small percentages however make a very very big difference in baking and cooking. Also avoid "European Style" butters they're from corn fed too, to be truly European they need to be pasture fed.
You might have also inadvertantly used one of any number of fake butters sold in America which aren't dairy products at all. There are also fake milk products called milk but they're not milk at all, more a "milk like drink". These have huge lists of ingriedients that may or may not include fresh milk or dairy fat.
Unfortunately the consummer is often dupped by these products. After all something calling itself 100% butter or 100% milk should indeed be butter or milk but the FDA doesn't agree.

thank you so much for taking the time to share this knowledge.

Companies put water in milk.
What I can see everywhere is that butter is no longer yellowish, it is getting whiter and whiter, and softer,
even the most expensive ones
(some cheaper butters are from the same company)

the expensive ones are "better" but because cheaper butters are so bad, expensive butters don't have to be good anymore.

It's all a damn manipulation by the dairy companies.

And to top it all, it is a product that is harmful to health and its production pollutes our planet!!!

It does matter...and I am getting sick of being manipulated. The butter does sputter and does not brown. Not a good thing if you are making Brown Butter Sugar Cookies. The butter did not foam, but developed scum on top of what looked like it was curdled. One and one half sticks of butter magically became 1 cup of melted YELLOW liquid after ONE HOUR of trying to brown it. I have been baking for many years and know what I am doing. No wonder younger women don't want to learn to cook...nothing is what it once was. Messes with your recipes, especially baking.

slaw et al- plse disregard my response above. i had not yet read the linked article. sorry.

smslaw is right--80% butterfat is the minimum required for USDA Grade A butter. If you look on the package, it will say what Grade the butter is. European butter like Plugra will list the USDA Grade and the grade it was given at production in its home country. You are unlikely to find anything lower than Grade A at a traditional grocery store--but if you buy Amish butter, it is ungraded and tends to have more water in it. Likewise, raw butter is not graded and will be less consistent. Small farms will not be subject to the same grading process as a large operation like Kraft or Land O' Lakes, and in some cases are omitted from the USDA grading process altogether because individual states license and monitor small family farms.

Wow...did you ask a great question! Have'nt we all suffered from sputtering butter.

i think kbc might have had a pc invasion of the little ones?

This article analyzed the percentages of fat, water, and milk solids in different butters, then tested several recipes with different butters to see what practical difference it made. The results are interesting. The variations in moisture content seem quite small, but even small variations can produce significantly affect results.

http://www.sfgate.com/recipes/article/When-Put-to-the-Test-Here-s-How-Butter-Brands-3236719.php

All butter you buy at the store has between about 15 and 20% water (80% fat is the legal minimum.) Unsalted supposedly has a bit less water. I wouldn't assume that a store brand has less fat content than a national brand. Almost all have the minimum 80% fat. Higher fat content makes pastry flakier. The difference between 15% water and 20% water can be significant. I'd check with the manufacturer and ask about specific moisture content. Plugra, for example, says it is 82% fat.

I just bought a store brand of unsalted butter to try it, and I found the same thing.I made buttercream and it ended up in the trash, there was too much water in the butter, it broke and I couldn't get it to come together, ended up in the trash, Thats the last time I deviate from the butter I always use. I wish I had an answer, just wanted to commiserate.