Some brands 'wet up' much more easily than others. The good thing about tubes is that they provide quantities of moist rich colour which is ideal for mixing big strong washes. They have their little pitfalls, such as drying out in very hot climates, having caps that stick or won't screw on properly. Tubes can also split and burst - some brands are worse than others. Despite these problems tubes are universally popular.
Some artists squeeze good quantities of tube paint into the wells of their palette.
They leave the paint to dry, then re-wet it when they need to use it. Others purchase pan sets and when a pan is empty they squeeze tube paint into the pan and leave it to dry. Some brands, depending on their composition, respond more favourably than others to this treatment. Put simply, watercolour paints are coloured pigments suspended in a medium. In the manufacture of artists' paints.