In the short term it is regulated by baroreceptors which act via the brain to influence nervous and endocrine systems. Blood pressure that is low due to a disease state is called hypotension, and pressure that is consistently high is hypertension. Both have many causes and may be of sudden onset or of long duration. Long term hypertension is a risk factor for many diseases, including heart disease, stroke and kidney failure.
Decrease your sodium intake. An excessive amount of salt in the body will absorb water and cause you to retain water. Consequently, to avoid water retention, moderate the amount of sodium you eat on a daily basis. Many processed foods are high in sodium, and will cause you to exceed your daily recommended sodium intake.
Some common causes of water retention include sitting or standing for a long time, eating salty foods, allergies, insect bites, infection, hormonal changes during menstruation and pregnancy, high or low blood pressure and as a side effect to some medications.