I found a site that sells Cistern Gauges that you can fix on any location in the house, that measures the waterlevel that is still in the cistern and it installed in 10 minits. a real bargain
take a look at http://www.cisterngauges.com
It saved me lots of back pain lifting the concreat manhole and now I will never have a broken pump again.
Greets Monique