sources of drinking water as a result of the system's storm surge and fresh water flooding. Tuvalu is affected by perigean spring tide events which raise the sea level higher than a normal high tide. The highest peak tide recorded by the Tuvalu Meteorological Service was on 24 February 2006 and again on 19 February 2015. As a result of historical sea level rise, the king tide events lead to flooding of low-lying areas, which is compounded when sea levels are further raised by La Niña effects or local storms and waves. In the future, sea level rise may threaten to submerge the nation entirely as it is estimated that a sea level rise of 20–40 centimetres (8–16 inches) in the next 100 years could make Tuvalu uninhabitable. Tuvalu experiences westerly gales and heavy rain from October to March – the period that is known as Tau-o-lalo; with tropical temperatures moderated by easterly winds from April to November. Drinking water is mostly obtained from rainwater collected on roofs and stored in tanks; these systems are often poorly maintained, resulting in lack of water. Aid programs of Australia and the European Union have been directed to improving the storage capacity on Funafuti and in the outer islands. Borrow Pits Remediation (BPR) project When the airfield, which is now Funafuti International Airport, was constructed during World War II. The coral base of the atoll was used as fill to create the runway. The resulting borrow pits impacted the fresh-water aquifer. In the low areas of Funafuti the sea water can be seen bubbling up through the porous coral rock to form pools with each high tide. Since 1994 a project has been in development to assess the environmental impact of transporting sand from the lagoon to fill all the borrow pits and low-lying areas on Fongafale. In 2013 a feasibility study was carried out and in 2014 the Tuvalu Borrow Pits Remediation (BPR) project was approved, so that all ten borrow pits would be filled, leaving Tafua Pond, which is a natural pond. The New Zealand Government funded the BPR project. The project was carried out in 2015 with 365,000 sqm of sand being dredged from the lagoon to fill the holes and improve living conditions on the island. This project increased the usable land space on Fongafale by eight per cent. Environment – international agreements Tuvalu is a party to: Biodiversity,