Thanks everyone for the ...

Thanks everyone for the responses!

To give some more details about the situation: we are targeting roughly 30 000 households in 2 communities. Many of these tanks are open top and uncovered. About 50% of them are made of plastic, the other 50% are made of cement (and most of the cement tanks are uncovered because of where they're placed). The majority of households in one community are receiving less than 3 hours of piped water a day, so they are primarily relying on stored water. Some households have a separate tap for drinking water, so they may be drawing from that tap during the times water service is available and storing it separately. Our survey on drinking water sources gave us conflicted data - almost all HH claim to be using piped water, but validation sessions suggest that a number of them may be buying bottled water.

There are no detailed studies on the piped system as this is an old and extremely volatile area where the municipality is afraid to enter. Household connections are all unpaid for and privately made - there is no documentation on these.

Roughly 13% of HH we surveyed stated that they treat their water. Most use boiling. Chlorine tablets and filters are too expensive here, and they are not widely available.

This project is primarily hygiene promotion, so there is no technology component. We are setting up building-level WASH Committees to inform residents about tank disinfection, among other things.

We ended up supplying WASH Committees with large bottles of Javel (3.5% active chlorine) because that is the most widely available household chlorine in the market. The procedure we taught them was to use detergent to clean the outside and inside of the tank. They were taught to mix a disinfecting solution by diluting the chlorine to 100 mg/L. The solution was applied to the inside surface of the tank, which was to be kept wet with the solution for 1 hour (they would have to wipe the inner walls of the tank with the solution several times over the course of the hour to make sure of this). This minimized the amount of water needed to clean the tanks and the higher chlorine concentration shortened the amount of time.

Afterwards, they were to flush it out 2 times or until they could no longer smell the chlorine from their taps.

We taught them this two weeks ago, and we have so far heard that one committee has done some tank cleaning but we have not gotten a detailed report about how they did it. More monitoring will be happening over the next few weeks to see how much this procedure was taken up.

Tanks range from 40 L to 1000+ L in capacity. Chlorine testing strips are very expensive here. There are no community tanks - most surveyed households have individual tanks and a few have none at all.

We're finalizing the baseline assessment report, and I can post a link up with the details of the situation when its completed. This will hopefully pave the way for an actual water treatment project.