A new council housing complex on Dominick Street Lower, scheduled to be completed this year, will capture rainwater in tanks on the roof and pipe it into the homes to flush toilets.

That’s a design feature that should be found in all new apartment buildings, said Robert Moss, the green communities programme manager with An Taisce.

“It makes sense,” he said on the phone on Monday. “It rains a lot in Ireland so why not make use of it?”

Around a quarter of the treated water used by households is used to flush toilets, said Moss, in a presentation to councillors at a meeting of the council’s climate action, environment and energy committee on 25 May.

Using rainwater instead would help cut waste and cut carbon emissions by saving electricity.

Rainwater harvesting could also help protect against flooding and pollution when it rains heavily, he says.

“Every time there is a major rainfall event all of that wastewater goes into the sewerage system and it overflows,” says Moss.

If some more were caught and put to use, there would be less to overload the sewers and cause overflows from Ringsend into Dublin Bay.

The council should install water meters in the new complex at Dominick Street to track the water savings from the rainwater-harvesting system there, Moss says.

Councillors who sit on the committee said they supported Moss’ idea of using the new complex at Dominick Street as a pilot project for the city.

How Does It Work?

Dublin City Council is building 72 new homes as part of a regeneration of council housing at Dominick Street Lower in the north inner-city.

On Tuesday morning, construction workers in yellow hard hats were powerwashing the pavement outside a new five-storey red brick building.

The homes in the new flats at Dominick Street Lower look nearly finished. The project is scheduled for completion by the end of June this year, says a recent council report.

Sixty-seven of the 72 new homes will flush their toilets using harvested rainwater, said Moss, in his presentation to the climate action committee.

He showed councillors a simple diagram that outlines how rainwater is collected on the roof of the building, filtered and runs into a storage tank, which has an overflow pipe. A mains pipe also flows into the tank so if there isn’t enough rainwater the mains water can top it up, he said.

The council has committed in its Climate Change Action Plan to “research feasibility of rainwater harvesting in Council buildings and social housing”.

The council should use Dominick Street Lower as a pilot project to track the impact of rainwater harvesting on water use, said Moss.

To do that, it should install water meters, says Moss. “We have a case study now so let’s measure it and see what it does.”

If the rainwater-harvesting system works well then the council should say in its next city development plan that new apartment complexes must include them, he says.

Independent Councillor Mannix Flynn said Moss had made a strong case for building rainwater harvesting into future council housing.

“I would suggest that this committee would endorse Dublin City Council looking at this presentation favourably and that we would initiate a pilot scheme,” said Flynn.

Dublin City Council didn’t respond in time for publication to queries sent Monday about whether it plans to roll out rainwater harvesting in its new apartment complexes in the future.

A Look at Savings

If all the apartment complexes in Dublin incorporated rainwater harvesting into their design that could save an estimated 1 million to 1.5 million litres of treated water each year, said Moss.

That is tiny though compared with the amount of water households use. It’s just 0.021 percent of the daily national domestic water demand in 2019, he says in his presentation.

Ireland is currently the only EU country that doesn’t charge for water, he said.

The EU water framework directive says there should be charges for treated water, he says. “So we are in breach of that and it’s not sustainable.”

Rainwater harvesting also reduces carbon emissions, because electricity is usually used to treat water and to pump it to where it is needed – but that’s not necessary when it’s collected from the roof and gravity-fed into the toilet tank.

Moss says he estimates that if all the apartment complexes in the city harvested rainwater the carbon savings could be somewhere in the region of 350,000 kg to 538,000 kg each year.

Again that is a very small proportion of the overall usage, he says.

Floods Ahead

Reducing wastewater and carbon emissions would be welcome, says Moss. But the main benefit of harvesting rainwater would be reducing flooding and the pollution floods can cause.

Dublin has a combined sewage system, so during heavy rain, the sewers overflow into the wastewater system and the mix ends up in streams, rivers and eventually beaches.

The options for how to address this problem are limited. There is very little green space around the inner city to soak up the rain – although that is something the council is working to change.

“You can’t really put in any sustainable urban drainage around an apartment complex in Dublin 1,” says Moss. “It’s a concrete jungle.”

So when it rains heavily there is nowhere for the rainwater to go except the sewers. “It goes to Ringsend and causes the water treatment plant to overflow and pollute Dublin Bay,” he says.

Fine Gael Councillor Naoise Ó Muirí asked whether there is a grant system in place to retrofit existing complexes with rainwater harvesting. Moss said that he isn’t aware of any.

Retrofitting all the existing apartment complexes in the city to incorporate rainwater harvesting would be a major operation, said Moss on the phone on Monday.

What the government should do is immediately change the building regulations for new homes, he says. “It needs to be in the building regulations now.”

The Department of Housing didn’t respond in time for publication to queries sent on Tuesday about whether rainwater harvesting should be brought into the building regulations.

Laoise Neylon is a reporter for Dublin Inquirer. You can reach her at lneylon@dublininquirer.com.

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