Found this on the web http://www.leptospirosis.org/
Filtration - does not work!
Leptospira are incredibly small - they can pass through the pores in water filters, even those that claim to remove bacteria. They will pass easily through filters with a pore size of more than 0.2 micron, including membrane and charcoal types. High-pressure laboratory filters with a pore size of less than 0.1 micron will block them, but the typical hand-held water filters used by hikers, pool filters and the fitted cannisters used in some domestic kitchen applicanes are useless at removing leptospires - they are often used to separate leptospires from other bacteria when preparing samples for research, as the leptospires pass through but other bacteria don't!
UV sterilisers
These are also very effective against leptospira (and most other pathogens), and can be bought on all scales. Permanent systems for processing flowing water in a domestic house are available, but can be expensive and use electricity. Portable devices for camping and backpacking are also available, resembling a small flashlight or pen, and these can be used to sterilise a single cup of water - but need batteries. The advantage of using UV is that there are no chemicals involved, and the electricity required is less than for boiling the same volume. It does require the sample to be transparent though, so can't be used on things like milk
Cheers David