TOXIC chlorine should only be stored at Bristol Water's Purton site for one more year.

Water works bosses explained the developments to their purification processes at a meeting to reassure residents about the company’s safety procedures.

Bristol Water came to speak to villagers at a public meeting at St John the Evangelist Church in Purton last week after receiving a letter from concerned resident Bob Ealing.

Local people felt that they had been kept in the dark about the processes at the Purton Water Treatment Works and expressed worries about the safety of the village in the event of a chemical accident.

Every Monday at 12pm the emergency klaxon is tested and local people have received instructions on what to do in the event of a real emergency, which includes remaining indoors, away from the windows.

But villagers were concerned that visitors to the canal were unaware of the protocol. Built in the 1970s, the treatment works filters water from the Gloucester and Sharpness Canal and the River Frome and supplies around half of Bristol’s water supply.

Alan Marvin, production director at Bristol Water, explained that the company had reduced the amount of liquid chlorine kept on site from the original 50 tonnes in the 1970s to just seven tonnes of chlorine. Sulphur dioxide, which used to be kept in equally large volumes, is no longer needed on site at all.

Ten years ago, ozone was introduced to the treatment process, which reduced the need for the other chemicals, which are dangerous when concentrated amounts are breathed into the lungs.

And if Bristol Water move to on-site electrolytic chlorination next year, they will be able to produce their own bleach at Purton, eliminating the need to bring any chlorine onto the site.

The low-concentration bleach, about one or two per cent compared to 15 per cent in household bleach, disinfects the pipes and taps that water travels in to people’s homes.

Mr Marvin and his colleague Phil Marshall told the meeting that as well as having detailed plans to deal with an emergency, the company also had their own chemical response unit.

But they stressed that the amount of chlorine held on site currently was extremely unlikely to cause harm if there was a serious leak.

Mr Marvin said: "The bottom line is that even a severe leak of chlorine in the volume that we have wouldn’t be significantly dangerous at the boundary of the site.

"When you start getting out to 1,000 metres, then the dispersion factor of that is so great, the reality is that you could smell chlorine, probably, but it wouldn’t be dangerous to you."

Residents who attended the meeting seemed largely satisfied with what they heard.

Retired mechanical engineer Ian Harris said: "It struck me that he (Mr Marvin) did a very good job of placating the audience. With advancing technology, safety is improved."

Villager Margaret Price added: "I think in the beginning we were all very worried about visitors and especially the young people that come with canoes.

"When we get these leaflets saying, ‘Go indoors, shut the windows,’ we were thinking what we would do about them.

"There still isn’t any provision for it, but by this time next year it should all be solved."

Long-time Purton resident Mr Ealing agreed, saying: "The problem is still there, but the future looks promising."