  Detection of the electromagnetic emission from coalescing binary neutron
stars (BNS) is important for understanding the merger and afterglow. We present
a search for a radio counterpart to the gravitational-wave source GW190425, a
BNS merger, using Apertif on the Westerbork Synthesis Radio Telescope (WSRT).
We observe a field of high probability in the associated localisation region
for 3 epochs at 68, 90 and 109 days post merger. We identify all sources that
exhibit flux variations consistent with the expected afterglow emission of
GW190425. We also look for possible transients. These are sources which are
only present in one epoch. In addition, we quantify our ability to search for
radio afterglows in fourth and future observing runs of the gravitational-wave
detector network using Monte Carlo simulations. We found 25 afterglow
candidates based on their variability. None of these could be associated with a
possible host galaxy at the luminosity distance of GW190425. We also found 55
transient afterglow candidates that were only detected in one epoch. All turned
out to be image artefacts. In the fourth observing run, we predict that up to
three afterglows will be detectable by Apertif. While we did not find a source
related to the afterglow emission of GW190425, the search validates our methods
for future searches of radio afterglows.
