They do not remove 100 percent of the color or odor from water. They require reatively non-turbid water to function properly. They cannot function if they are frozen. Water must be added regularly and the sand must stay covered by water continuously. During construction care must be taken to prevent air pockets from forming in the sand – this will foul the filter and require removing the sand and removing all anaerobic bacteria and odors. Industrial pollution is only partially removed from water by these filters. These filters must be allowed to “ripen” (have water flow through them for at least 3 weeks) before they will purify water. They are VERY heavy (1000 pounds plus) and much thought must go into where they will be located – it is almost impossible to move them once they are set up. back to top 5.