Disinfecting areas of ground, ponds or water features

When dealing with areas of open ground or water, disinfection is a lot more complex than for small objects or interior surfaces. The first issue is of carrier control, as there’s no point in trying to clean an area if the bacteria are being shed by animals visiting it every night. Rodent and small mammal control is an industry in itself and not a subject we intend to comment on, so seek out your local council or pest control company and go from there. The animals are only visiting because of food and shelter, so getting rid of those will also help.

Flowing water (rivers, springs, etc.) cannot be chemically treated at source, so if the water is being abstracted for drinking it needs to be disinfected at that stage, not while still running across the ground. Seawater is not an issue as leptospira can’t survive in that much salt, and in some cases this has been used as an inexpensive chemical treatment for ornamental ponds and garden features, but where the water contains fish or aquatic plants it is almost impossible to treat with chemicals. Swimming pools and some water features will use chlorination tablets, and these are very effective but of course lead to a smell inside buildings, whereas using brine does not (although it will increase corrosion). For large ponds and lakes, chemical treatment is impossible as the volumes required would be dangerous to life nearby and damage the environment.

Freshwater springs used to supply drinking water (for houses and campsites) should be sealed from source if possible (easy enough for a borehole, less for resurgences) to avoid contamination from all causes, not just leptospires. The bacteria can survive for several months or years in the right conditions, so in some cases water pumped from very close to the surface may allow percolation from rainwater to carry urine and bacteria directly into the abstraction zone. The percolation time for a location can easily be measured by dye-tracing.

Areas of wet soil (especially clays) can retain enough moisture for the bacteria to survive for several months, and this is often essential to maintain infection in carrier species that have a seasonal lifestyle, but for humans presents risks from swampy areas, rice-fields and when digging deep excavations. Dry ground will be safe, so in warm dry weather the surface levels will become safe very quickly even if the bacteria are able to survive deeper.

Hard surfaces such as concrete rapidly dry out, and so are of no significant risk except during prolonged periods of rain. This means that the risks for urban areas with most surfaces covered are far lower than for rural locations, but it depends more on climate and season than on anything else. During dry hot weather the bacteria will only survive in bodies of water (rivers and lakes), so the ground becomes safe. Winter conditions are also of lower risk as the bacteria do not tolerate the around-zero temperatures and repeated freeze-thaw cycles, plus carrier animals are less active. The highest risk is during rainy, temperate or tropical conditions where the ground remains wet and animals are active.