Water butts are brilliant for saving some water for the garden. I’ve lost count the amount of times i’ve actually seen issues like this where they haven’t been installed correctly and issues like this occur. Suspended timber floors can flood, block and beam floors can flood, and solid walls without a damp proof course can get rising damp issues. If suspended timber floors get very damp, perhaps the moisture balance could be pushed towards dry rot and wet rot issues occurring.
Make sure you read the instructions on how to install these correctly to prevent the above happening. If you do have a damp issue, and require a damp survey/investigation give us a shout 🙂