Flood
During a flood there is plenty of water logging and overflow of water,  it is mostly polluted and not safe to drink. If people drink this dirty water, they may suffer from diseases such as typhoid and cholera, hepatitis and other such diseases. People can get ready to survive a flood by filling many containers with fresh and clean drinking water and storing other emergency supplies; like: medicine and food. During flood people try to go to higher sides because the flood water wouldn't reach high areas. Also drains overflow and mix with clean water and people who drink it might fall ill.