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If there are small worms that are visible to the naked eye then you need some sort of filtration in addition to chlorination. The filtration could be a simple gravity sand filter or a ceramic filter.
A sand filter could be made out of in an oil drum filled with sand. Water would flow in at the top and be collected from the bottom. Part of the treatment comes from biological action by bacteria that develops in the top layer of sand (exposed to sunlight) and this would clog up periodically and have to be replaced.
Chlorination would be necessary. There are guidelines in several books that I have at home but unfortunately I am currently working in Namibia. They are probably in the RedR book "Engineering in Emergencies". It depends on the volume of water and the strength of the chlorine used. Water should be allowed to stand for a few hours after chlorination to allow the chlorine time to kill bacteria before it is drunk.
Regards,
Martin