Norwalk virus, Winter vomiting disease

Illegal entry to body via hand to mouth or air exposure, causes watery diarrhoea and vomiting.

At home in the guts of mammals, loiters around schools, childcare centres, nursing homes, cruise ships, and other crowded environments.

Highly contagious, causes mild disease if you are generally healthy, severe under other circumstances.

Practice hand hygiene, avoid contaminated water sources, wash fruits and vegetables before eating, check your shellfish is from clean water, be more vigilant in winter.

“Beaver fever”, giardiasis

A sneaky little protozoan parasite that loves to crash your water party, spreading through faecally-contaminated drinking or recreational water.

Loiters in untreated or poorly treated water from lakes, rivers, swimming pools, springs, ponds, and streams. Can even sneak into municipal water supplies.

Causes giardiasis (a mix of diarrhoea, stomach cramps, nausea, dehydration and smelly gas!). Especially mean to kids and those with weaker immune systems.

Municipal water is generally safe, but if you're concerned, use a certified water filter, boil your water, and avoid swallowing poorly or untreated water.

Weil's disease, Leptospirosis

A bacterium that sneaks into the body through cuts, abrasions, and sometimes through the eyes, nose and mouth, after direct contact with urine from infected animals or through contaminated water, soil or food.

Found in the urine of infected animals (e.g. pigs, mice, rats, cattle, dogs and humans), loiters in kidneys, loves warm, moist climates.

Causes the disease leptospirosis. Symptoms include headache, fever, bleeding, muscle pain, chills, red eyes and vomiting. Without treatment, can lead to kidney and liver damage, meningitis and even death.

Take care in warm moist climates including contact with soil and vegetation. Do not swim if you have cuts or abrasions. Do not swallow water when swimming. Avoid water contact after floods or cyclones. Do not drink untreated water.

Cyanobacteria, Blue-green Algae

Fixing nitrogen one minute, poisoning your water the next - spicing things up with a side of toxins, making your water unsafe for drinking, swimming, or even watering your garden! Also known to instigate the occasional fish-kill party through oxygen depletion.

Found naturally in every moist environment such as damp soils, lakes, ponds and slow moving rivers.

Skin irritation and allergic reactions to severe liver, neurological damage and animal deaths. Toxins are implicated in cancer.

Pay attention to public health advisories, do not swim or allow your pets to access water subject to high risk alerts, be aware of and do not enter water with ‘musty’ smells and surface scums, do not drink untreated water.

PFCs (perfluorinated compounds), Per- and Poly-fluoroalkyl Substances, “Forever Chemicals”

Sneaky entry to the body, mainly through the mouth or nose, squats in the liver, kidneys, blood and fat.

Fire-fighting foams, personal care products (such as shampoos, make-up and dental floss), some packaging, and can turn up in dust, water sources, soils and foods.

Implicated in some cancers, reduced fertility, developmental delays in kids, reduced immune status, cholesterol and obesity problems (depends on amount consumed).

Drinking water is generally safe (but check with your supplier), avoid stain-resistant coatings, check your personal care products, avoid non-stick pans, avoid eating seafood from impacted waters.

“Swamp perfume”, “wet socks”, MIB

Leaving a bad taste in your mouth and a musty smell in your glass. MIB doesn’t make you sick – but it sure makes your water unwanted.

Found chilling with algae and bacteria in lakes, reservoirs, and water tanks. Loves warm weather and nutrient-rich waters.

Although non-toxic, makes safe water seem unsafe. It’s tough to get rid of – regular treatment doesn’t faze it – keeping water crews busy and budgets stretched.

If it’s too hard to swallow, use an activated carbon filter to catch MIB before it hits your mouth.