Watching TV Zattoo uses about 1.3 GB of data per hour for each stream of standard definition (SD), and up to 2.2 GB per hour for each stream of HD quality.
In the Zattoo app-settings on Android and iOS, the bitrate can be changed from high to low and vice versa. Setting the bitrate to low is recommended when using Zattoo in mobile network.
At a low bitrate, the volume of the data one uses is limited to 900 kbps. Data consumption is then reduced to around 400 MB per hour.
This is how to set bitrate to high/low on your iPhone/iPad:
Open Zattoo app > Go to Settings > Bitrate > mobile/WLAN > high/low