Instant water tester

[HLHJ]

Instant test for spores (giardia), bacteria, some viruses in a water stream or container. Detects particles down to 1μm in diameter. Tests filters, streams, solar stills. You'd have to let the sediment settle out first.

[rickj]

It should not be too difficult to detect particles, even quite small ones. The awkward part would be classifying them. I'm not certain how we could distinguish potentially harmful particles, such as Giardia spores, from harmless dust particles.

[HLHJ]

I don't think it has to distinguish -- if there are no Giardia-sized particles, there is no Giardia. Most filters work on this principle, and just testing whether the filter has worked would be useful. Some spring- and well-water is also remarkably well-filtered by the rock it has percolated through; the device could confirm that this water is safe.

A readout of the size distribution of particles might also make it useful for hydrography, sediment analysis and flood work. How do people currently measure sediment profiles of watercourses? The one time I did it, we scooped up sediment, took it back to the lab, baked it dry, and sieved it into fractions, which we weighed. This was useless for the finest fractions, which blew away. This method may not be state-of-the-art, though.

[rickj]

Since we need only particle size, it may be better to back-light the sample, then produce a magnified image for analysis. In this way the emissivity of the particles does not matter.