Hello, thank you for taking the time to post your question!
The conversion factor that you want to use here is that 1 kg = 1L and then 1L = 0.264172 gallons
So to convert you want to take
823,000 kg x 1 kg/L x 0.264172 gal/L = 217,414 gallons of water
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)