Question: The New River, a London waterway opened in 1613, supplies drinking water from the springs of which river?
Context: The Castanhão Dam (Portuguese: "Açude Castanhão" ) is a dam in the state of Ceará, Brazil.  It is the largest multiple use reservoir in the country, the largest on an intermittent river, and the main reservoir for the state and the metropolitan region of Fortaleza.  The dam supplies drinking water, and supports industry, irrigation and fish farming.  Through steady release of water the dam maintains water flow in the Jaguaribe River throughout the year.  During 2012–16 Ceará experienced a prolonged drought.  Water levels in the reservoir dropped to 5% of capacity and usage had to be rationed. Water scarcity or lack of safe drinking water is one of the world's leading problems affecting more than 1.1 billion people globally, meaning that one in every six people lacks access to safe drinking water.  The Joint Monitoring Programme for Water Supply and Sanitation set up by the World Health Organization (WHO) and United Nations Children's Fund (UNICEF) defines safe drinking water as "water with microbial, chemical and physical characteristics that meets WHO guidelines or national standards on drinking water quality."  Hydrologists generally assess water scarcity by looking at a population-to-water equation that treats 1,700 cubic meters per person as the national threshold for meeting water requirements for agricultural and industrial production, energy, and the environment.  Availability below the threshold of 1,000 cubic meters represents a state of "water scarcity", while anything below 500 cubic meters represents a state of "absolute scarcity". London's water supply infrastructure has developed over the centuries in line with the expansion of London.  For much of London's history, private companies supplied fresh water to various parts of London from wells, the River Thames and in the three centuries after the construction in 1613 of the New River, the River Lea, which has springs that divert alongside Hertford at an elevation of 40 metres AOD.  Further demand prompted new conduits and sources, particularly in the 150 years to 1900 as the Agricultural and Industrial Revolution caused a boom in London's population and housing. The River Lea in England originates in Marsh Farm, Leagrave, Luton in the Chiltern Hills and flows generally southeast, east, and then south through east London where it meets the River Thames, the last section being known as Bow Creek.  It is one of the largest rivers in London and the easternmost major tributary of the Thames.  Its valley creates a long chain of marshy ground along its lower length, much of which has been used for gravel and mineral extraction, reservoirs and industry.  Much of the river has been canalised to provide a navigable route for boats into eastern Hertfordshire, known as the Lee Navigation.  While the lower Lea remains somewhat polluted, its upper stretch and tributaries, classified as chalk streams, are a major source of drinking water for London.  A diversion known as the New River, opened in 1613, abstracts clean water away from the lower stretch of the river for drinking.  Its origins in the Chilterns contribute to the extreme hardness (high mineral content) of London tap water. Australia is one of many countries that have water fluoridation programs currently operating (see Fluoridation by country).  As of March 2012, artificially fluoridated drinking water is provided for 70% or more of the population in all states and territories.  The acceptance of the benefits of water fluoridation occurred in Australia in December 1953, roughly two years after acceptance in the United States.  Many of Australia's drinking water supplies subsequently began fluoridation in the 1960s and 1970s.  By 1984 almost 66% of the Australian population had access to fluoridated drinking water, represented by 850 towns and cities.  Some areas within Australia have natural fluoride levels in the groundwater, which was estimated in 1991 to provide drinking water to approximately 0.9% of the population. The Saco River is a river in northeastern New Hampshire and southwestern Maine in the United States.  It drains a rural area of 1703 sqmi of forests and farmlands west and southwest of Portland, emptying into the Atlantic Ocean at Saco Bay, 136 mi from its source.  It supplies drinking water to roughly 250,000 people in thirty-five towns; and historically provided transportation and water power encouraging development of the cities of Biddeford and Saco and the towns of Fryeburg and Hiram.  The name "Saco" comes from the Eastern Abenaki word "[sɑkohki]", meaning "land where the river comes out". " The Jesuit Relations", ethnographic documents from the 17th century, refer to the river as "Chouacoet". Starina reservoir is a water reservoir in eastern Slovakia, Snina District, located in the Poloniny National Park.  It is the most important source of drinking water in the area, built on the headwaters of the river Cirocha.  Building started in 1981.  3,463 inhabitants were evacuated from 769 dwellings from the 7 following villages (Starina, Dara, Ostrožnica, Smolník, Ruské, Veľká Poľana and Zvala).  The total surface of the water reservoir Starina is 240 ha.  The height of the water headbay is 50 m.  This source of drinking water is very important because it supplies nearly whole area of East Slovakia with drinking water.  There is a scenic viewpoint above the water reservoir Starina. Eibenstock Dam (German: "Talsperre Eibenstock" ) near Eibenstock in the Ore Mountains, Germany, is the largest dam in the Free State of Saxony in terms of the height of the dam above the valley floor, and its reservoir is the largest in volume in Saxony.  The dam impounds the waters of the Zwickauer Mulde and supplies drinking water to the region of Chemnitz and Zwickau, as well as providing flood protection, delivering extra water during times of drought and, to a lesser extent, generating electricity from hydropower.  Its dimensions make it the second largest drinking water reservoir in Germany's new federal states. The Stillwater River is part of the Nashua River watershed.  This river is part of the Massachusetts Water Resources Authority system that supplies drinking water to the greater Boston area. The New River is an artificial waterway in England, opened in 1613 to supply London with fresh drinking water taken from the River Lea and from Chadwell Springs and Amwell Springs (which ceased to flow by the end of the nineteenth century), and other springs and wells along its course.
Answer: River Lea