Ballroom dancing watercolor painting

I have continued with my ballroom dancing watercolor painting last night.  I found that as I paint everyday, I have easily make mistakes either on the watercolor wash, the choice of color, the wetness of the paper etc.  It is a continuous learning process and without risking making mistakes, I won't be able to learn.
Last night I have learnt that the pure watercolor from the tube can get 'dirty' by mixing with dirty water.  You also have to watch out for the unclean brush too.  Last night I loaded my brush with some water from my brush cleaning water, dip into Winsor Yellow and mix it in my palette before putting on the paper.  On the palette it looks nice and bright and I even try it on a piece of scrap watercolor paper before I apply it on my painting.  But after I finished painting a large area with that mixture, I found that it is really muddy compare with the ones I did the night before.  It was the water I use to mix the paint with.  The water is from the night before and it was the brush cleaning water I am using.  Now I know it is wise to keep two jars of water for my watercolor painting, one clean one for mixing and one for cleaning brushes with.
The lession I have learned from my mistake is the quickest way to get muddy watercolor and easiest way to waste brilliant watercolor pigment.  Those two would give you dull and opaque watercolor and should be something to avoid in our daily watercolor painting.  Love to hear from those who have similar experience.