I have drank from springs, rivers, and lakes all untreated and in retrospect, it was not smart and I was unaware of the dangers; I turned out fine the doctor said the brain ameba probably starved.
To answer the question directly
"What should I do if I am worried after ingesting untreated water?"
Write down the time and date you ingested it.
The course of treatment
if something happens will all be responding to that timestamp, and you can mostly determine what is causing an illness by knowing when symptoms started.
There is a risk of disease-causing microbes or parasites, with parasites normally being much worse.
You should start feeling symptoms if something is wrong in 1 hour to 3 days for illness from disease-causing microbes.
Here is what the CDC says for drinking water risks:
Health effects of consuming water with disease-causing microbes.
Most life-threatening waterborne diseases caused by microbes (such as typhoid fever or cholera) are rare in the United States today. The more common illnesses caused by viruses, bacteria, and parasites can result in stomach pain, vomiting, diarrhea, headache, fever, and kidney failure. Infectious diseases such as hepatitis can also occur. Hepatitis may be severe in people with weakened immune systems (e.g., infants and the elderly) and sometimes fatal in people with severely compromised immune systems (e.g., cancer and AIDS patients).
CDC Water Safty Information
If you start to feel any of those symptoms you should contact your doctor, explain your issue from the water, note the time and date, and get on an anti-biotic.
Don't sweat it, your body is capable of fighting off a lot of things, now is not a great time to educate yourself about rat-lung-worm. Make sure to document how you feel, take your own temperature, and eat some leafy greens and filtered water.