No Topic Sentence

Here is another example where a paragraph without a topic sentence is hard to understand:

Only the new lever control system needs to be purchased to effect the switch to easier tap operation. The retention of conventional tap washer in this design also allows for lower costs. This design would be sold as either an individual lever system or a whole tap unit, so that a user could either convert their current tap, or install the whole unit as a new tap. Alternatively new houses could be equipped with the whole tap unit during construction.

Compare the previous paragraph to this one.

Formulating a clear topic sentence will help you to establish the information that should be included in your paragraph.