Another kind of a filter is manufactured by English manufacturers and called their "Low Pressure Water Filter". It is practically a cistern filter, as this illustration will show.

The water to be filtered passes up through the bottom of the filter and can be drawn in a continuous flow through the pipe leading to the draw-off cock. The . filtering substances are composed of materials which act chemically and mechanically upon the impurities contained in solution in the water and require renewing after a certain period. This is easily done by disconnecting the top, when the old filtering material can be taken out, and a fresh charge put in. The filtering medium is chalk, sand, lime. Asbestos and charcoal may also be used. Another kind of filter with upward filtration is shown in this illustration.

Fig. 33.   Low Pressure Water Filter for Cisterns

Fig. 33. - Low-Pressure Water-Filter for Cisterns.