Food, water, and what to do when something didn't sit right.

Most foodborne and waterborne illness follows a recognizable timeline. The shape of the first 24 hours, the second 24, and the third tells you most of what you need to know about whether you can stay home, call telehealth, or head to urgent care. This guide walks the timeline and pulls out the patterns that change the tier.

Hour 0-6: "something I ate"

The first hours are usually the loudest. Sudden nausea, cramping, vomiting, and a vague sense of dread within an hour or two of a specific meal point most strongly toward a bacterial-toxin food poisoning (pre-formed toxins from staph or Bacillus cereus). Intense but short.

• Stop eating solid food. Sip small amounts of water or an electrolyte solution.
• Note what you ate, when, and who else ate it. Important if more people get sick or you need to report it later.
• Resist the urge to take anti-diarrheals in the first hour. Letting the body clear the toxin is usually right.

Hour 6-24: peak

This is usually the worst stretch. Vomiting, diarrhea, cramping, low-grade fever, and exhaustion are common. The single most useful safety metric is hydration, not symptom intensity.

• Sip frequently. Small, frequent volumes are absorbed better than large gulps when nauseated.
• Oral rehydration salts beat plain water when losses are heavy. Sports drinks are a distant second.
• Do not push food. When you can keep fluids down for two to three hours, try crackers, plain rice, banana, or toast.
• Rest. Sleep is part of treatment.

Hour 24-72: stabilization or escalation

By hour 24, the picture should be improving. Vomiting has eased, you can keep small meals down, energy is creeping back. If that is the trajectory, you are almost certainly through the worst of it. If symptoms are flat or worsening, this is the window where the tier changes.

• Hydration trending the right way: continuing urination, less dizziness on standing, mucous membranes no longer parched. Stay the course.
• Hydration trending the wrong way: not urinating for many hours, deep yellow urine, persistent dizziness, dry tongue, lethargy. This is a telehealth or urgent-care call.

Day 3+: it is still going

Most viral GI bugs and most bacterial food poisoning are largely done in 72 hours. Symptoms past day three are a different conversation. Possibilities include a more serious bacterial infection (Salmonella, Shigella, Campylobacter, certain E. coli), a parasitic cause, or something unrelated to the meal you blamed.

• Persistent diarrhea past 72 hours, especially with fever or blood, deserves a clinician visit and often a stool test.
• After international travel, parasitic causes such as Giardia become more likely. Mention the travel.
• If symptoms relapse after seeming to resolve, that pattern is worth flagging.

Hydration as the dashboard

Throughout the timeline, your hydration tells you more than your symptoms do.

• Urine color: pale straw is good. Deep yellow or amber means you are behind. None at all for many hours is a red flag.
• Dizziness on standing: a brief head rush is common. Persistent or repeated near-fainting signals meaningful volume depletion.
• Dry mucous membranes: sticky tongue, cracking lips, dry eyes. These show up before more obvious signs.
• Skin turgor: a gentle pinch on the back of the hand should snap back instantly. Slow recoil suggests dehydration.
• Lethargy: unusually flat affect, hard to rouse from sleep, or a child who is "not themselves."

Patterns that change the tier

• High fever (101 F or above) lasting more than 24 hours.
• Blood in stool, bright red or black and tarry.
• Severe abdominal pain, especially localized to the lower right or upper right quadrant.
• Persistent symptoms past 72 hours with no improvement, or relapse.
• Inability to keep any fluid down for more than 12 hours.
• Higher-risk individuals: infants, older adults, pregnancy, immunocompromised. Escalate sooner. Pregnancy raises the stakes for listeria, salmonella, and severe dehydration.

Bacterial toxin vs viral GI vs parasitic

You usually cannot tell at the symptom level, but timing offers clues.

• Bacterial toxin (staph, B. cereus): onset 1 to 6 hours. Sudden, intense, often short. Vomiting prominent.
• Viral GI (norovirus, rotavirus): onset 12 to 48 hours. Diarrhea and vomiting both prominent. Highly contagious in households.
• Bacterial infection (Salmonella, Campylobacter, E. coli): onset 1 to 5 days. Often fever, sometimes blood in stool. Longer course.
• Parasitic (Giardia, others): onset 1 to 2 weeks, often after travel or wilderness water. Bloating, persistent loose stools, weight loss.

Domestic water concerns

• Boil-water notices. Boil for at least one minute (three at altitude) for drinking, cooking, and tooth-brushing. Use bottled water for infants. Showering and dish-washing are usually still fine.
• Cloudy or off-tasting tap water without a notice. Contact your water utility; it is usually a flushing or maintenance issue, not an emergency.
• Lead in older homes. Real concern in housing built before 1986. A home test or filtered water (NSF/ANSI 53 certification for lead) is reasonable for cooking and drinking.
• Well water. Test annually for bacteria and nitrates, and after any flooding, septic issue, or unusual taste. Your county environmental health office can point you to certified labs.

Travelers' diarrhea

• In areas with unfamiliar water systems, default to bottled or boiled water for drinking and tooth-brushing.
• Avoid ice from unknown sources, raw produce washed in tap water, and undercooked seafood or meat.
• Carry oral rehydration salts. They take almost no space and can change the trajectory of a bad day.
• Talk to a travel-medicine clinician before high-risk trips about whether antibiotic standby therapy is appropriate for you.

Food allergy vs food poisoning

• Food allergy: usually within minutes to two hours of eating. Hives, swelling (face, lips, tongue), wheezing, throat tightness. Can progress to anaphylaxis. Epinephrine and 911 if breathing or circulation are affected.
• Food poisoning: usually hours later, GI-dominant, rarely involves hives or breathing problems.
• If multiple people who shared a meal got sick, food poisoning is more likely. If only the person with a known allergy reacted, allergy comes first to mind.

Reporting suspected outbreaks

If several people got sick from the same source, reporting it is a real public service. Local health departments use these reports to investigate and prevent further cases.

• For suspected restaurant or commercial food, call your local or state health department. Search "[your state] foodborne illness report."
• For packaged foods, you can also report to the FDA.
• Save leftovers in a sealed bag in the fridge for a few days; investigators sometimes ask for samples.

Monitor, seek help, escalate

• Monitor at home: nausea, vomiting, or diarrhea for under 48 hours, low-grade fever, normal urination, able to keep some fluids down. Hydrate, rest, simple foods.
• Seek help (telehealth or urgent care): fever above 102 F lasting more than 24 hours, persistent symptoms past 72 hours, blood in stool, inability to keep fluids down for 12+ hours, signs of meaningful dehydration, any concern in an infant, older adult, pregnant person, or immunocompromised individual.
• Escalate to emergency care: severe abdominal pain, vomiting blood, black tarry stool, signs of severe dehydration (no urine output, confusion, fainting), high fever with neurological signs, or any sense that something is seriously wrong.

Related: Exposure Hub, Travel Risk, Stomach Symptoms.