• Question: when water becomes unsafe because of harmful bacteria, how does that spread?

    Asked by Anita xx on 18 Jun 2025.
    • Photo: Samuel Bloomfield

      Samuel Bloomfield answered on 18 Jun 2025:

      Harmful bacteria in water often originate from human waste or farm run-off (water that flows over farms and picks up animal waste). These bacteria reach rivers and streams that flow into each other. Humans that swim or play in the water can then be exposed to these harmful bacteria.

    • Photo: Caroline Mullen

      Caroline Mullen answered on 19 Jun 2025: last edited 19 Jun 2025 13:53

      It depends on the water, if it is still water like a pond or lake things can spread really easily as nothing is stopping them getting around the area, in running water like rivers and streams the water in constantly moving out to sea so bacteria have less chance of sticking around. Anything near sewage inputs or farm inputs can have some harmful bacteria in it, so be careful when planning where to go for a dip!

    • Photo: Karen Edwards

      Karen Edwards answered on 30 Jun 2025:

      Good question. Basically, the bacteria are moved with the water. So, if they are in a river, they will move downstream with the water. The bacteria are probably also growing and multiplying but the good news is that they have a short life cycle so will also be dying.

Comments

  • Photo: melissau

    melissau commented on :

    When thinking about how bacteria may be passed from one human (or animal) to another human (or animal) it’s important to learn about transmission routes so that you can think about how to minimise the risk of infection. An example of a bacterial infection which is transmitted via water is leptospirosis, which originates in rats and found in their urine. If an infected rat’s urine gets into a river, for example, this can infect a human (or any other animal, for example a dog) who goes swimming in the river or even puts their hand (paw) into the river or drinks from the river as the leptospirosis bacteria can enter the human/dog body via a cut on your skin or via mucous membranes which line the inside your mouth. In the UK vet will routinely offer to vaccinate a dog against leptospirosis if the owner says that the dog likes to go swimming in fresh water or goes walking in woodlands/fields where it might come into contact with rats’ urine. People are not generally vaccinated for leptospirosis, but this is a risk to be aware of if you like to go swimming in the river or if you do sports like kayaking/paddle boarding which make it likely that you’ll fall into the water.