disclosed is a porous filter support plate of the kind used in traveling bridge filters for the support of granular filter media used in the filtration of waste water , industrial liquors or baths , or for filtration of potable water in a water purification system . the support plates are formed of porous , heat - fusible materials , for example , a thermoplastic organic material , joined together by heat - fused butt joints and / or reinforced by vertical zones which extend vertically through the plates in which the material has been brought to a molten state and is pressed together to form a dense , solid , non - porous mass .