how do i make is so that the puddle of water makes the player slide, in ohter words make it into a slippery surface?

heres my movement code

using UnityEngine;
using System.Collections;

public class PlayerController : MonoBehaviour {

public float speed;

private Rigidbody rb;

void Start ()
	rb = GetComponent<Rigidbody>();

void FixedUpdate ()
	float moveHorizontal = Input.GetAxis ("Horizontal");
	float moveVertical = Input.GetAxis ("Vertical");
	Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
	rb.AddForce (movement * speed);


Use a Physic Material:


Tutorial Video