So that the artificially created stream in the garden does not dry up after a while, you must seal its subsurface waterproof. This also applies to streams made of concrete, because the material draws water and is also attacked by constant moisture. There are various possibilities.
The concrete stream must be sealed well
How to waterproof a concrete stream
There are numerous materials that can be used to make streams watertight. For a stream made of concrete you need additional means that keep penetrating moisture away. The following four options are often used.
Pond liner / liquid liner
Sealing the concrete stream bed with pond liner is just as practical as it is inexpensive. If you don't want to bother laying the film carefully, you can use the liquid version. This can simply be spread or sprayed onto the dried and hardened concrete, is phenol-free and completely harmless to humans and animals - this is particularly important in streams that lead to a fish pond.
epoxy resin
In contrast to the black pond liner, epoxy resin is colorless and not only seals concrete, but also streams made of wood or natural stone. The material is viscous and can therefore be spread easily.
sealing slurry
Sealing sludge or sealing sludge, as used for sealing house walls and cellars, has also proven to be practicable for artificial streams. This material is mixed with water, applied to the hardened and dried concrete and then left to dry. Sealing slurry is available as a two-component material and can also be used to fill cracks and other damaged areas in the concrete stream bed.
sealing powder
In contrast to the other sealing materials, so-called sealing powder is not applied to the concrete foundation that has already dried, but is instead mixed into the cement mixture before construction. The use of this mortar additive saves you another operation, but has a lesser effect. Sealing powder only reduces water absorption, but cannot make the concrete completely waterproof.
tips
Actually waterproofing concrete is a lot of work and requires accuracy. Instead, you can simply do without the concrete and just lay out the stream with pond liner. This also allows you more flexibility, after all, concrete structures are difficult to correct once they have dried.