How to Stop from MoveTowards then Move again

So I got an Object that cannot go to Water, if by chance he collide to Water he will stop. I have done that so that it will stop, but cannot seem to find a way to make it move again. I also wanted if he can actually move again, if i clicked on the other side of the water he will not move pass the water.

I was using NavMesh back then but because my work wanted me to not using NavMesh I cannot seem to find a way to do it.

Code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Vector : MonoBehaviour
 {
     public static Vector instance;
     public Transform obj;
     [SerializeField] Vector3 a;
     [SerializeField] Vector3 b;
     [SerializeField] Vector3 c;
     public Transform water;
     public float speed;
     private RaycastHit hit;
     Vector3 previousPosition;
     Vector3 targetPosition;
     float lerpMoving = 1f;
     public List<Transform> selectedUnit = new List<Transform>();
     private Vector3 mousePos;
     public bool insidetrigger = false;
     public float stopdistance = 5;
     public bool onwater = false;
 
     // Start is called before the first frame update
     void Start()
     {
         instance = this;
     }
 
     void Awake()
     {
 
     }
 
     // Update is called once per frame
     void Update()
     {
         // transform.position = obj.position;
         HandleUnitMovement();
     }
 
     public void HandleUnitMovement()
     {
         if (Input.GetMouseButtonDown(0))
             {
                 mousePos = Input.mousePosition;
                 Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
                 
                 if (Physics.Raycast(ray, out hit))
                 {
                     LayerMask layerHit = hit.transform.gameObject.layer;
 
                     switch (layerHit.value)
                     {
                         case 8:
                             SelectUnit(hit.transform, Input.GetKey(KeyCode.LeftShift));
                             break;
                         case 10:
                             SelectUnit(hit.transform, Input.GetKey(KeyCode.LeftShift));
                             break;
                         default:
                             // isDragging = true;
                             DeselectUnit();
                             break;
                     }
                 }
             }
 
         if (Input.GetKeyDown(KeyCode.Mouse1) && HaveSelectedUnit()) 
         {
             if (Input.GetMouseButtonDown(1) && selectedUnit.Contains(obj)) 
             {
                 Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);          
                 if (Physics.Raycast(ray, out hit)) 
                 {
                     LayerMask layerHit = hit.transform.gameObject.layer;
 
                     switch (layerHit.value)
                     {
                         case 4:
                             break;  
                         case 8:
                             break;
                         case 9:
                             break;
                         default:
                             foreach(Transform unit in selectedUnit)
                             {
                                 previousPosition = transform.position;
                                 targetPosition = new Vector3 (hit.point.x, previousPosition.y, 
                                 hit.point.z);
                                 lerpMoving = 0;
                             }
                             break;
                     }   
                 }
                 else
                 {
 
                 }
             }
         }
 
         if(lerpMoving < 1)
         {
             movePlayer();   
         }
     }
 
     public void movePlayer()
     {
         if(!onwater)
         {
             lerpMoving += Time.deltaTime; 
             transform.position = Vector3.MoveTowards(previousPosition, targetPosition, 
             speed * lerpMoving);
 
             if(Vector3.Distance(obj.position, water.position) < stopdistance)
             {
                 onwater = true;
                 // yield return null;
             }
         } 
         else if(onwater)
         {
             lerpMoving += Time.deltaTime; 
             transform.position = Vector3.MoveTowards(previousPosition, targetPosition, 
             speed * lerpMoving);
         }
     }
         
     private void SelectUnit(Transform unit, bool canMultiselect = false)
     {
         if(!canMultiselect)
         {
             DeselectUnit();
         }
         selectedUnit.Add(unit);
         unit.Find("Highlight").gameObject.SetActive(true);
     }
 
     private void DeselectUnit()
     {
         for (int i = 0; i < selectedUnit.Count; i++)
         {
             selectedUnit[i].Find("Highlight").gameObject.SetActive(false);
         }
         selectedUnit.Clear();
 
     }
 
     private bool HaveSelectedUnit()
     {
         if (selectedUnit.Count > 0)
         {
             return true;
         }
         else
         {
             return false;
         }
     }
 
 }
 

Here's my map

The Object in question is the cube