Using tap water for sinus rinses is generally not recommended. Tap water may contain impurities, bacteria, or other microorganisms that can be harmful if introduced into your nasal passages. 

The safest option for nasal irrigation, such as with a neti pot or nasal rinse, is to use distilled or sterilized water. Distilled water has gone through a process of boiling and condensation, which removes impurities and contaminants. Sterilized water, such as water that has been boiled and then cooled, can also be used. 

If you don't have access to distilled or sterilized water, you can use water that has been properly filtered and treated with a water purifier specifically designed to remove microorganisms. You should follow the manufacturer's guidelines for using water in your particular sinus rinse device. 

Using water that is not adequately purified or sterilized may increase the risk of infection, particularly if you have a compromised immune system or are prone to sinus infections. 

Always remember to use the proper technique when performing nasal irrigation to minimize the risk of complications and follow any instructions provided with the nasal rinse device. If you have any doubts or concerns, consult with your healthcare provider before starting nasal irrigation.