Speed of precipitation of the weighed substances, including particles of the unspherical form easily determined experimentally, use as criterion describing the size of particles (hydraulic coarseness). Usually heterogeneous systems formed by insoluble in water impurities, are polydispersious, - they contain particles differing by the sizes or hydraulic coarseness. For the characteristic of such systems on the basis of results of the dispercial analysis distribution of particles on the sizes or weights is done. Such curves have the maxima indicating the prevailling contents in the given system of particles of the certain sizes, and in one source of water disperciality of the weighed substances can change in 2-3 times depending on the season of the year. Alongside with reservoirs with a rather large suspension (10-30 microns) there are sources, in which the insoluble impurity forms systems that are close to colloid ones (0,5-1,0 microns). Water in them is clarified only after upholding within several months.