1. I always found history as dull as ditchwater.

2. The lecture was as dull as ditchwater.

3. This novel is as dull as ditchwater, it doesn't have any decent plots.

4. The book I've been reading is as dull as ditchwater, it has no story or any interest at all.

5. No changes would be made and you would have nothing to fight against. Life would be as dull as ditchwater.

6. I tried to read her latest book but found it as dull as ditchwater.