Colloidal particles of metal oxides form deposits
on their containers. These deposits tend to sorb
dissolved impurities from the water. Therefore it is
important to design sampling systems so that the
buildup of metal oxide deposits is minimized. Reference
6 shows that the optimum velocity is 5 to 7
ft/s (1.5 to 2.1 m/s). In this velocity range, deposition
and erosion stabilize at a constant value after 30
days of operation. See Section 4 for further discussion
of sample line deposition