The Connors demonstrating a clay pot biological sand filter
(Photo: (c)Connor/CMS)

Once dirty water has been given to the nadi every day for two to three weeks, the filter will function effectively so long as the sand is not disturbed.

During this period the water will gradually improve. If the sand and stones were well washed, water can be improved a little by the filter even on the first day.

The nadi for storing clean water should be emptied every three days during this initial period while water quality is rapidly improving.

Pots for storing clean water should never be used for collecting dirty water.

When using a new nadi to make a filter, it should be first checked for leaks which should be repaired using cement.

Never completely fill a new nadi or small cracks will develop. Only half fill it with water at first, then after two or three hours, fill it completely and check for leaks.

If the filter gets too slow or stops working, remove the top few inches of sand from inside the nadi. Wash the dirt out of this sand with water in a bucket or bowl and then put it back in the nadi.

Make sure that the level of the sand in the nadi is restored to 5 inches below the bottom of the pipe where it comes through the side of the nadi.

When it becomes necessary to clean the sand in the filter it is good if there is another filter in the community that can be used for the two or three weeks it takes for the filter to build up its numbers of good microbes after being cleaned.

Dirty water used for starting off a new or recently cleaned nadi can be put through the new one, then through an established one if it is necessary to drink this water.