Water companies are often required to cover reservoirs with roofs, if only to not adversely affect the landscape of the local area.

On other occasions, it may be a case of stopping contamination from getting into the clean water reservoir. When a reservoir is required to have a roof placed over it, more often than not an impermeable lining system is needed to protect the water from contaminants that can leak in through the roof into the water supply.

The material used can vary a great deal depending on the individual needs of each project, from a 2.0mm HDPE membrane, to a 1.0mm Polypropylene membrane, as used on Denton Service Reservoir.  This project involved ELS installing 56,000m² of 1mm Polypropylene, a 12mm Geocomposite drainage layer, and a geotextile protection layer.