Using watercolor as a medium is quite unique, since you only use water and some pigments. Since you activate the paint when you start painting, it would seem logical to be able to reactivate it. Is that possible?
Watercolor paint can be reactivated with water since it stays water-soluble even after drying. If you make a mistake, you can use this to erase certain sections of the painting. It can also be used to mix dried up paints with other colors.

What is the best way to reactivate watercolor?
As watercolor stays water-soluble even after it has dried up, it is the only medium that can be reactivated.
Because of its unique nature, it can be simply reactivated with water.
Oils and acrylics simply cannot accomplish this. Acrylic and oil paints can, however, be painted over while completely covering the paint beneath, which isn’t possible with watercolor, so every artist has to pick their preferred medium.
Let’s now move on to the guide on how to activate watercolor.
Before you begin, you will need water and a brush. The brush should be a bit smaller than the area you wish to activate.
Now it’s essentially the same process as if you were using dried up paint on a palette.
The first thing you need to do is dip the brush in water and squeeze it out a bit. In order to control the water more effectively, your brush should not be entirely wet, but rather damp.
You have to be very careful now when applying the brush to the paper. Your brush should not drip water or anything else, as this will leave spots on your painting.
Go to the area you want to reactivate and gently press the brush onto the paper. You should swirl it around a bit if the area is larger.
Your paint is now reactivated. There are two main options that you could choose. I’ll discuss both of them now, so keep reading.
On a side note: If you’d like to find out, whether you can flatten a watercolor painting by ironing it, you should check this article out.

Reactivating watercolor to erase it
The first option you can try is to reactivate the watercolor to erase it. This is probably the option you will use most often.
The first thing you need to do is follow the process I just described.
Now, you’ll need an additional brush or a tissue. I prefer to use a brush since it’s more precise and won’t tear.
In order for it to soak up the water on the paper, the additional brush must be dry or very close to being dry.
After reactivating the area you would like to erase, you will have to soak up this water and paint mixture with the dry brush and therefore lift it off.
You must be very surgical about this so as not to erase too much.
Usually, doing this once won’t completely remove the paint. That’s fine if you plan on painting it over with a dark color.
If you want to use another bright color on top of it, such as yellow, orange, etc., you can just repeat the same process.
However, you should be careful not to use too much water, so the paper does not tear or loose its stability.
You should also always try to soak up all of the water you apply to the paper, so you don’t leave too much water on the paper, which would spread and erase too much.
Keep in mind that you must soak up the paint / lift it off with a pretty dry brush in order to get as much paint on it as possible.
If you’d like to learn more about framing watercolor paintings, I’d recommend reading this guide.
Mixing dried up watercolor
This process is similar to the previous one, except that you add paint instead of erasing it.
The first step is to reactivate the paint, as I explained in step 1.
There are now two ways to do this. Either you use just one brush and reactivate the dried up paint with a brush that already has paint on it, or you use two brushes, one for reactivating and the other for mixing and applying new paint.
You should try both to see what you like most and what best suits your style.
Let’s take a closer look at each process.
Using one brush to mix dry paint
If you want to use this method, you would need a brush that’s a bit smaller than the area you’d like to mix, so you have some room to actually mix the paint on the paper.
Basically, you’ll do the same thing you would when painting normally. Wet your brush and pick up some paint from your palette.
You should also make sure that you don’t have too much water on your brush, so it doesn’t drip all over your painting.
It is now just a matter of following the same steps as erasing. Mix the paints up using the brush by pressing it onto the area you wish to paint and swirling it around. It’s that simple.
Using two brushes to mix dried paint
In this method, you don’t use a dry brush as a second brush, but rather one with paint on it.
By using brush one, which is full of water, you need to reactivate the paint and by using brush two, you need to mix the paint on the paper.
As a beginner, only use a small amount of water and paint on brush 2, since it is hard to estimate.

When reactivating watercolor, what should you be cautious of
As I mentioned before, there are basically only two things to watch out for.
The main factor is your water usage. You should not use too much water on your brush because it will become hard to control and might reactivate more paint than you intended.
It would be better to take more steps than trying to do everything at once.
Please test out either of the methods mentioned above on a doodle painting first, so you don’t ruin a finished piece if something doesn’t work out.
Additionally, I would advise being careful with how much you press onto the paper with your brush, as too much force might tear it over time.
To learn more about watercolor painting, you should also read Do Watercolor Paints Have Fumes and Can You Use Watercolor On Sketch Paper?
Summary
Water can be used to reactivate watercolors. You could either erase parts of your painting or mix new colors with dried up paint using this method. This can be done by using one or two brushes and a bit of water.