As I understand it is not an ...

As I understand it is not an artesian well.  The water is constantly running from a tap with people using buckets to catch the water.  If you want to calculate volume loss it will be an estimate. 

Checking flow from source:  You need to measure the flow using a known volume and measuring the time in seconds to calculate flow.  Lets say 20l bucket takes 10 seconds to fill.  Thus it will be 2ls/.  To estimate the waste check the time between people changing between getting water from the source and get an estimate for the day.

 

The second method is to dig a hole at the outlet and measure the waste there.  It will also just be a daily estimate.

 

Stand pipes with taps are definitely an answer.  It will also be more hygienic.  Show the people that it is important to close the tap after usage.  A few tap will also ensure that people do not waste time to wait for other for water.  In South Africa in the old days the women fetch water and it was there time to get together.  The time lost was actually good for the woman to correspond with each other.

As I understand it is not a artesian well