Cleaning the nose by flushing with saline (salt) water mixed in a certain way is very helpful for people with colds or allergies. Special spray bottles or neti pots may be used.
However, if you live in a warm climate and amoeba contaminate the water, failure to use filtered or boiled water may kill you due to an infection with the amoeba causing encephalitis. You must let boiled water cool before using it. Temperature of the water is important as cold water will cause pain and headache.
It is CRUCIAL that you carefully follow directions about using CLEAN water and not tap or stream water.
Two deaths have recently been reported due to encephalitis caused by amoeba contaminating water used to flush noses- read here
For more information about available products (neti pots and sinus flushing systems) go to company web sites here (SinuCleanse [registered trademark]) and here (NasoFlo [registered trademark]) and elsewhere.