There was a dead rat/etc. in my water tank. What do I do?

Rats and other carrier species accessing domestic water tanks or the reservoirs of untreated springs, either alive or dead, are a significant problem as although the individual probability that an animal carries dangerous strains of leptospira is low (typically 10 to 20 percent), the bacteria will survive for several weeks or months in clean cool water and so present more of a risk than rodent activity on household surfaces or dry food. Although the decomposition of a dead animal in air will cause changes in acidity that eventually kill the bacteria still present in the carcass, if the animal is immersed in water the bacteria will migrate from the body and survive provided the water is within the acceptable range of environmental limits (and drinking water will always be within that range).

Water tanks and pipework should be cleaned and flushed to remove any residual contamination. Your local state public health service will be able to advise on what action to take, but typically the process of disinfecting a domestic water supply is not difficult, and uses a very weak acid or antibacterial solution flushed slowly through the pipework, followed by clean water to flush out the chemical. The bacteria are very sensitive to acids and disinfectants, so treatment can use concentrations that present no human health hazard. The tank should of course be secured so the problem doesn’t happen again. Hot water used solely for heating need not be treated, but the bacteria are perfectly capable of surviving in clean water at up to 40 °C and so hot water systems that operate at below 60°C can present a risk if the water is used for drinking. The bacteria cannot reproduce at these high temperatures and so will naturally expire over time.

While waiting for the water system to be disinfected, water can be made acceptably safe for drinking by boiling it for five minutes. This will also manage the risks from other bacteria or viruses carried on or in the animal.

In terms of medication, the normal regime for at-risk exposure of this form would be to either wait for symptoms, or provide a single antibiotic dose called a prophylactic. Which method will depend on the specifics of each case, as to the likelihood of infection and the ages of the people involved.