When I went to Portugal this last trip, 99% of there water was from Cisterns. The water from the Cistern was clear and I treated it with a steripen every time I drank out of it, we joked about a fish was living in it but other than that it's been there for over 30 years of hard use everyday and supplies most of the water for everything from washing cloths, drinking, bath,etc.. I'm a firm believer of them and I would definitely build one above ground and enclosed for ease of maintenance with filters and solar UV as was suggested by Nicodemus. They are a great source of off the grid dependable water that taste great, just rough filter it and UV treat it and everything would be fine.

Water is tapped off the roof and delivered in this above ground enclosed concrete cistern and is almost always full all year. They said it is really rare it drys up but they live on a island that rains all the time. Over 30 years of hard use 24/7.

Failure is not an option!
USMC Jungle Environmental Survival Training PI 1985