Conductivity of liquids (3D resistor network)
Resistivity is measured in (Ω⋅m). But you should think of the single distance measurement as "area over distance". Area over distance is m^2/m, which reduces to m. So resistivity goes up linearly with distance, and down linearly with cross-sectional area.

So if your tap water is 264µS/cm ~= 3800Ω.cm, then there is 3800Ω of resistance for every cm of distance through a water column with a cross-sectional area of one square cm. Double the length of the water column and the resistance doubles. Double the cross sectional area of the water column and the resistance halves.

If you stick with a water path that has a cross sectional area of one square centimetre, then if the path reduces to 2mm long, the resistance will be 760Ω. At 1mm it will be 380Ω.

Of course, practically speaking it would be very hard to control the cross-sectional area, and even if you could there's likely to be all sorts of edge effects as you start to get down to smaller distances. But at least that should help you understand resistivity.