One of the solutions would be to use “Blending Medium” by Winsor&Newton. This medium “Slows the drying of water colours, allowing more time for blending. Extends working time even in hot climates.”. Add a few drops to your water jar and if you don’t see the different add more until you notice the difference in the drying time.
Another way, if you don’t have access to the blending medium, is to add a few drops of honey to your painting water.
Glycerine is a humectant just like honey. You can use glycerine in the same way as honey.
You can also extend the paint and water drying time by adding several drops of ox gall to your painting water. Ox gall primarily enhances the paint mixing and blending capabilities to achieve beautiful smooth washes, but it also helps to keep the paint wet a bit longer.
Alternatively, you can adjust your way of painting to the conditions. You can make use of the fact that the layers dry quickly to paint in glazes. But I can imagine it would be hard to do with every painting and it can be frustrating, so treat it just as fun exercise.