Cambridge's school strikers have agreed to hold a future strike on the Cam water emergency following a talk given to the group by Stephen Tomkins, the chair of the Cam Valley Forum Group and emeritus fellow at Homerton College, on the mistreatment of the Cam and chalk hills in the region.

A water shortage is now on the cards for the region, Mr Tomkins told the youth group, because there are too many boreholes sunk into the chalk deposits around the city - and they're drying up from decades of overuse.

"Cambridge gets its water from the tap," he told Cambridge Eco Schools Council at the Michaelhouse Centre on Saturday (October 5).

"What comes out of the tap comes from the water treatment centre in Milton and before that it comes from the chalk hills which run right through Cambridge to Royston. From April to September the rain doesn't go into the rocks but in winter it goes into the ground and that's where the water companies get your water. That's fine, but there are many more people here not than there used to be.

"About 300 years ago Thomas Hobson wanted to bring clean water into the city. Water was brought by conduit right through to Market Square and you could have a bucket or two from that source. By 1850 water was sourced from Fulbourn village - then on wetland - and was dug from the ground. In 1920 they went up to Fleam Dyke and dug another borehole. That lasted until 1950 and now there's dozens of bore holes dug into the chalk. With the dry winters we have had recently the streams are beginning to feel the stress.

"This spring was the Environment Agency recorded the lowest level of water for 40 or 50 years.We're taking too much water. There's a problem."

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The talk concluded: "Don't worry too much about it because we will put it right. There's some very bright people working on the issue and don't forget wildlife bounces back very quickly as conditions improve. You can turn it around."

Co-chair Samaya Hone asked: "You said not to worry because people will come up with solutions, but what are the possible solutions?"

"The first one is to take less water from our chalk," replied Mr Tomkins. "Another is we do have a lot of rainfall to the west. Cambridge gets very very little rain. Water is very precious. Another is using less water per person."

Speaking after the session he said of the occasion: "I think they're lovely, they're a good bunch. I'm cautiously optimistic that good will come of it."

"Why only cautiously?" asked Rosanna Bienzobas, a parent of one of the council members.

"Water abstraction is not a right it's a privilege and water companies feel they own the water but they don't," Mr Tomkins said. "It belongs to the environment and they're licensed to take only a limited amount.

"Research shows people don't usually use much less water until the taps run dry. Water metering should be compulsory but we are also using more than 130 litres per head per day in Cambridge."

The water sector has additional problems because the Environment Agency both licenses the water and is responsible for cleaning up the environment, and the two roles aren't necessarily compatible. Plus there's another worry.

"Government departments have had their staff and funding decimated every year over many years. It's at the point now where the Environment Agency is unable to monitor the abuse of the environment."

This shocking state of affairs illustrates why investment/funding is urgent. Mr Tomkins cited the sewage programme as an example. "There's a lot going into the sewage works and they clean it up and the water goes back into the river at Milton. That water is not so bad but going out towards the river Nene they're not coping and it's failing the quality criteria for our rivers."

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Earlier in the day Extinction Rebellion staged a 'human logo' event on Parker's Piece, using people to create an XR sandglass with protesters dressed in sackcloth to represent sand, which went from one side of the iconic Cambridge location to the other to represent the movement of the grains from the top of the hourglass to the bottom "as the clock runs down".

That afternoon, XR's Bridges Banner Protest saw dozens of campaigners bedecking Cambridge's bridges with banners and other artwork illustrating the critical nature of the climate emergency, urging the governments of the UK and other nations to prioritise the reduction of the temperature on Earth - and inviting people to an international day of action in London on Monday as part of a global protest.

"Starting Monday October 7, for two weeks, Extinction Rebellion and allied movements will gather in major cities across the globe and continue to rebel against the world’s governments for their criminal inaction on the climate and ecological crisis," says the group.