diff --git a/code/src/models/hydrological_model.py b/code/src/models/hydrological_model.py
index 1563a65..cb26ca5 100644
--- a/code/src/models/hydrological_model.py
+++ b/code/src/models/hydrological_model.py
@@ -67,9 +67,9 @@ def pressure_head(self, theta, z):
 
         # Check the input dimensions (of the vertical domain).
         if dim_d != z.shape[0]:
-            raise ValueError(" {0}: Input size dimensions do not match:"
-                             " {1} not equal to {2}.".format(self.__class__.__name__,
-                                                             dim_d, z.shape[0]))
+            raise ValueError(f" {self.__class__.__name__}:"
+                             f" Input size dimensions don't match:"
+                             f" {dim_d} not equal to {z.shape[0]}.")
         # _end_if_
 
         # Get the porosity field at 'z'.
diff --git a/code/src/models/vanGenuchten.py b/code/src/models/vanGenuchten.py
index 0871321..d5d982f 100644
--- a/code/src/models/vanGenuchten.py
+++ b/code/src/models/vanGenuchten.py
@@ -52,9 +52,9 @@ def __call__(self, psi, z, *args):
 
         # Check the input dimensions (of the vertical domain).
         if dim_d != z.shape[0]:
-            raise ValueError(" {0}: Input size dimensions do not match:"
-                             " {1} not equal to {2}.".format(self.__class__.__name__,
-                                                             dim_d, z.shape[0]))
+            raise ValueError(f" {self.__class__.__name__}:"
+                             f" Input size dimensions don't match:"
+                             f" {dim_d} not equal to {z.shape[0]}.")
         # _end_if_
 
         # Get the porosity field at 'z'.
diff --git a/code/src/models/vrettas_fung.py b/code/src/models/vrettas_fung.py
index a1352a8..de22d22 100644
--- a/code/src/models/vrettas_fung.py
+++ b/code/src/models/vrettas_fung.py
@@ -80,9 +80,9 @@ def __call__(self, psi, z, *args):
 
         # Check the input dimensions (of the vertical domain).
         if dim_d != z.shape[0]:
-            raise ValueError(" {0}: Input size dimensions do not match:"
-                             " {1} not equal to {2}.".format(self.__class__.__name__,
-                                                             dim_d, z.shape[0]))
+            raise ValueError(f" {self.__class__.__name__}:"
+                             f" Input size dimensions don't match:"
+                             f" {dim_d} not equal to {z.shape[0]}.")
         # _end_if_
 
         # Get the porosity field at 'z'.