- mechanical failures such as a blocked drain, leaking roof, overflowing gutters
- accidents such as sprinkler system discharge, broken water pipe, fire
- natural events such as rainstorm, snow melt, slow-rising flood.
Buildings have to be well maintained, with regular checks to ensure that gutters and flat roofs are clear of all obstacles such as leaves, plastic bags, debris and dead birds.
Monitoring systems are in place in areas likely to cause flooding e.g. in AHU areas.