diff --git a/data/forcefield_section/H2O/SPC.sec b/data/forcefield_section/H2O/SPC.sec
index 896c6079f7..6c12bf34b4 100644
--- a/data/forcefield_section/H2O/SPC.sec
+++ b/data/forcefield_section/H2O/SPC.sec
@@ -3,6 +3,9 @@
     # https://doi.org/10.1021/j100308a038
     # Note: This force field requires a correpsonding &G3X3 constraint section
     #       in &MOTION / &CONSTRAINT
+    #       Alternatively, an unconstrained flexible variant of this force field can be defined
+    #       by setting the K parameters in the sections &BEND and &BOND to non-zero values.
+    #       Usage examples can be found in the folder cp2k/tests/Fist/regtest-water/.
     &FORCEFIELD
       &BEND
         ATOMS HW OW HW
diff --git a/data/forcefield_section/H2O/SPCE.sec b/data/forcefield_section/H2O/SPCE.sec
index 5ba700c213..2efe948573 100644
--- a/data/forcefield_section/H2O/SPCE.sec
+++ b/data/forcefield_section/H2O/SPCE.sec
@@ -3,6 +3,9 @@
     # https://doi.org/10.1021/j100308a038
     # Note: This force field requires a correpsonding &G3X3 constraint section
     #       in &MOTION / &CONSTRAINT
+    #       Alternatively, an unconstrained flexible variant of this force field can be defined
+    #       by setting the K parameters in the sections &BEND and &BOND to non-zero values.
+    #       Usage examples can be found in the folder cp2k/tests/Fist/regtest-water/.
     &FORCEFIELD
       &BEND
         ATOMS HW OW HW
diff --git a/data/forcefield_section/H2O/TIP3P.sec b/data/forcefield_section/H2O/TIP3P.sec
index 74bbe9691d..c7b58432f5 100644
--- a/data/forcefield_section/H2O/TIP3P.sec
+++ b/data/forcefield_section/H2O/TIP3P.sec
@@ -3,6 +3,10 @@
     # https://doi.org/10.1063/1.481505
     # Note: This force field requires a correpsonding &G3X3 constraint section
     #       in &MOTION / &CONSTRAINT
+    #       Alternatively, an unconstrained flexible variant of this force field can be defined
+    #       by setting the K parameters in the sections &BEND and &BOND to non-zero values, e.g.
+    #       see the file TIP3P_FLEXIBLE.sec.
+    #       Usage examples can be found in the folder cp2k/tests/Fist/regtest-water/.
     &FORCEFIELD
       &BEND
         ATOMS HW OW HW
diff --git a/data/forcefield_section/H2O/TIP3P_FLEXIBLE.sec b/data/forcefield_section/H2O/TIP3P_FLEXIBLE.sec
index d7550d3503..3460261019 100644
--- a/data/forcefield_section/H2O/TIP3P_FLEXIBLE.sec
+++ b/data/forcefield_section/H2O/TIP3P_FLEXIBLE.sec
@@ -1,17 +1,19 @@
     # TIP3P flexible water
     # M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000)
     # https://doi.org/10.1063/1.481505
+    # https://docs.lammps.org/Howto_tip3p.html
+    # Usage examples can be found in the folder cp2k/tests/Fist/regtest-water/.
     &FORCEFIELD
       &BEND
         ATOMS HW OW HW
-        K [kcalmol*rad^-2] 110.0
-        KIND harmonic
+        K [kcalmol*rad^-2] 55.0
+        KIND charmm
         THETA0 [deg] 104.52
       &END BEND
       &BOND
         ATOMS OW HW
-        K [kcalmol*Angstrom^-2] 900.0
-        KIND harmonic
+        K [kcalmol*Angstrom^-2] 450.0
+        KIND charmm
         R0 [Angstrom] 0.9572
       &END BOND
       &CHARGE
diff --git a/tests/Fist/regtest-water/H2O-SPC-6x6x6.inp b/tests/Fist/regtest-water/H2O-SPC-6x6x6.inp
index 72d8dcef4d..1132b0188f 100644
--- a/tests/Fist/regtest-water/H2O-SPC-6x6x6.inp
+++ b/tests/Fist/regtest-water/H2O-SPC-6x6x6.inp
@@ -173,6 +173,7 @@
       ELEMENT H
     &END KIND
     &TOPOLOGY
+      CONNECTIVITY generate
       MULTIPLE_UNIT_CELL ${na} ${nb} ${nc}
     &END TOPOLOGY
   &END SUBSYS
diff --git a/tests/Fist/regtest-water/H2O-SPCE-6x6x6.inp b/tests/Fist/regtest-water/H2O-SPCE-6x6x6.inp
index eb5e0c9f87..7f6423508a 100644
--- a/tests/Fist/regtest-water/H2O-SPCE-6x6x6.inp
+++ b/tests/Fist/regtest-water/H2O-SPCE-6x6x6.inp
@@ -173,6 +173,7 @@
       ELEMENT H
     &END KIND
     &TOPOLOGY
+      CONNECTIVITY generate
       MULTIPLE_UNIT_CELL ${na} ${nb} ${nc}
     &END TOPOLOGY
   &END SUBSYS
diff --git a/tests/Fist/regtest-water/H2O-TIP3P-6x6x6.inp b/tests/Fist/regtest-water/H2O-TIP3P-6x6x6.inp
index 409a88fcb1..931d509e28 100644
--- a/tests/Fist/regtest-water/H2O-TIP3P-6x6x6.inp
+++ b/tests/Fist/regtest-water/H2O-TIP3P-6x6x6.inp
@@ -173,6 +173,7 @@
       ELEMENT H
     &END KIND
     &TOPOLOGY
+      CONNECTIVITY generate
       MULTIPLE_UNIT_CELL ${na} ${nb} ${nc}
     &END TOPOLOGY
   &END SUBSYS
diff --git a/tests/Fist/regtest-water/H2O-TIP3P_FLEXIBLE-6x6x6.inp b/tests/Fist/regtest-water/H2O-TIP3P_FLEXIBLE-6x6x6.inp
index 00d4c6aa9e..7e3800749a 100644
--- a/tests/Fist/regtest-water/H2O-TIP3P_FLEXIBLE-6x6x6.inp
+++ b/tests/Fist/regtest-water/H2O-TIP3P_FLEXIBLE-6x6x6.inp
@@ -164,6 +164,7 @@
       ELEMENT H
     &END KIND
     &TOPOLOGY
+      CONNECTIVITY generate
       MULTIPLE_UNIT_CELL ${na} ${nb} ${nc}
     &END TOPOLOGY
   &END SUBSYS