system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is it that all these houses in the UK can hold back a river. Are all the doors completely watertight, and they have brick walls that let no water in at all? What is this sorcery?
gpt
Some houses, in some areas, where flooding has previously been a problem have adapted their houses to be much more watertight.

This involves sealing flaps over air vents and dams for doorways, and ensuring the toilet doesn't back up. Houses that have been extensively renovated after previous flooding will almost certainly have had all the wiring moved up above the expected flood level.

Brick walls are surprisingly watertight if they're in good condition. If they're not then you can waterproof them with sealant.

Of course - the best solution is to not live in a wet bit, but sometimes floods come along with cover areas previously never submerged.