How do i treat a runny nose?
There are a few things you can do to treat a runny nose:

1. Use a saline nasal spray or rinse to help clear your nasal passages.

2. Use a humidifier to add moisture to the air, which can help reduce nasal congestion.

3. Stay hydrated by drinking plenty of fluids, such as water and tea.

4. Use over-the-counter decongestants or antihistamines as directed by your healthcare provider.

5. Rest and take care of yourself to allow your body to heal.

If your symptoms persist or worsen, it's best to consult a healthcare provider for further evaluation and treatment.
For 2, is putting a glass of water on my heater good enough?
Putting an open container of water on a heat source will help increase the humidity in your room but not as quickly as a humidifier would.

You can increase the rate of evaporation by using a shallow bowl or tray rather than a glass to maximize the surface area. You could also use multiple bowls at the same time.

Please make sure you use bowls that are designed to be heated as others may break, creating dangerously sharp fragments. This risk is greatly increased if your heater operates at a high temperature which tends to be the case for older, smaller models.