By default, WhatsApp will automatically download images over your cellular connection to provide you with quick access to your latest photos.
To configure automatic photo, video or audio downloading, simply go to WhatsApp > tap More options > Settings > Data and storage usage > Media auto-download.
Here you can choose when WhatsApp will automatically download media.
Selected media will automatically download when you are connected to cellular data.
Selected media will automatically download when you are connected to Wi-Fi.
Selected media will automatically download when you are roaming.
Note: Enabling auto-download when roaming might result in significantly increased charges from your mobile provider as roaming data is often expensive.
Automatically downloaded media will show up in your gallery. If you want to stop all WhatsApp media from appearing in your gallery, we recommend that you create a .nomedia file or folder inside your WhatsApp images, audio and video folder. You can do this using a file explorer from the Google Play Store. If you change your mind later, you can simply delete the .nomedia file and WhatsApp media will show up in your gallery again.
Learn how to configure auto-download on: iPhone