1) Be aware that collecting and analysing water samples from a representative number of households is likely to be quite time-consuming and costly.
2) In acute emergencies it is often challenging to reach the standard of "no faecal coliforms per 100ml of water". Therefore, consult with the WASH cluster the possibility of changing your indicator to "... less than 10 faecal coliforms ...", reflecting the following thresholds described in UNHCR's Emergency Field Handbook:
> 0–10 faecal coliforms/100 ml = reasonable quality
> 10–100 faecal coliforms/100 ml = polluted
> 100–1,000 faecal coliforms/100 ml = dangerous
> 1,000 faecal coliforms/100 ml = very dangerous
3) BHA phrases the indicator slightly differently, as "percent of households whose drinking water supplies have 0 fecal coliforms per 100 ml sample".