Prevent access from outdoors. Keep windows and doors tightly closed. To allow fresh air into your apartment, use screens, as water bugs are unable to get through them. Use caulking to seal up any openings that may provide water bugs access, such as wall cracks and gaps around electrical outlets.
Mow the lawn often. If your apartment has its own lawn, keep water bugs away by frequent mowing and plant trimming. Cutting the grass gets rid of the natural living environment of a water bug, thus making it significantly less desirable for the pesky insects to come anywhere near your home.
Place chemical roach-bait traps outside your apartment. Position the traps around your apartment's exterior, especially near grass, windows and doors. Seek out a bait trap that is suited for larger roaches, since water bugs can sometimes be up to 2 inches in length.
Keep your apartment as clean as possible. Water bugs are attracted to open food sources and hiding spots that clutter provides. Vacuum your carpet to pick up any fallen bits of food. Take out the garbage frequently. The cleaner and less cluttered your apartment is, the less attractive it will be to water bugs.
Get rid of moisture. Moisture attracts water bugs, so make sure not to leave sinks wet. Fix any pipes that may be leaking. When you recycle soda cans and plastic bottles, rinse them out and dry them thoroughly before placing them in the recycling bin.