Since I have seen a number of recommendations for sinus rinse in this thread but haven't (yet) noticed this specifically mentioned: It is important to use sterile water if you are using water for the rinse. Water directly from the tap apparently may not be safe for that purpose (there was a case earlier this year where a person died from a brain eating bacteria - they were apparently infected from using unboiled tap water for a sinus rinse.)

https://www.healthywa.wa.gov.au/Articles/N_R/Nasal-irrigatio... https://www.everydayhealth.com/lung-respiratory/too-many-peo...