Water Conservation

Duncan Stewart’s Advice on Conserving Water in the Home

A) Ten Tap Tips: See Dublin City Council/Irish Water websites.

Click here http://www.taptips.ie/house-and-garden.htm 

B) My extra Tips:

1. General ways of reducing water waste:

Measure all typical uses of water in your home:

To check flow rate (L/minute) of showers and taps, use a 1L (litre) measure container and measure the time it takes to fill it.

Example: If a tap takes 10 seconds to fill a 1L container, then divide 1L by 10sec and then multiply by 60sec = flow rate of 6L/minute.

2. Smart use of water meter:

 Use a ‘Visual Display Unit’ in kitchen to read water meter, when wired to it – this  is not in use yet but has to happen if the Government is serious about water conservation.

3. Avoid wasting water:

 a) Leaky pipes: (public mains & private connections).

1% of houses have undetected leaks in their private connections, amounting to 15% of the total water provided in Ireland (1/3rd of the total leaks.)

    b) Dripping tap or WC cistern:

          A dripping pipe can use up to 0.05L/minute = 3L/hour =72L/24 hour.

If left go unrepaired, it would cost a whopping 26,280L/year. (Household allowance is 30m3/year).

This single drip would cost a household €128/year.

c) Use low-flow aeration/restrictors:

Fit aeration device on to showerhead and taps.

These can reduce flow by up to 30% to 40%

Saving water in toilets & bathrooms:

a) Shower - water consumption:

Power-shower: Pressure pumps for power showers use between 6L & 20L of water/minute.

A typical high-pressure power shower uses 17L/minute.

A wide ‘rain’ type showerhead (deluge) uses huge amounts of water.

Some showers have multiple nozzle outlets, which consume more.

Hot water also uses a lot of energy, which can cost about twice to three times that of the water used.

Regular low-pressure shower:

(Gravity fed from water storage tank in attic):

Flow rate=3L/minute. 3L x 3min=9L water. So a 5min shower =15L

Shower time can vary from 2mins to 10min. (some spend more time)

UK average shower length= 8.5minute shower.

(UK teenagers average 9.5minutes/shower)

Examples of shower use & cost of water:

Water charge= 0.488cent/L (for both services)

 3min low-flow shower: At 3L/min = 9L = 4.5cent

 5min power-shower: At 17L/min =85L =41cent.

 10 min power-shower: At 17L/min = 170L =83cent.

  Water cost of above for 365 days in year = €303/person/year.

  A family of four (using this amount of water each)= €1,210/year.

- Bath: A full bath uses 80litre of water. Water cost =40cent/full bath

-  WHB: Teeth brush: Taps use between 3 to 6L/min

So a 3minute teeth clean with a low flow tap running: 3min x 3L =9L= 4.5cent.

You can save water by turning the tap off while brushing teeth.

-  WC Cistern:

Old types: 10/12litre volume/flush.

= 60L/person/day=30cent/p/day (€110/person/year)

Dual-flush: =3litre & 6litre =Averages at 20litre/person/day=10cent/p/day (€36.5/person/year)

Solution for old WC cistern: Submerge a water displacement volume in cistern, such as  ‘hippo’ bags or bottles.

Or, lower the ball cock level in the cistern to reduce its volume.

4. Laundry:

Clothes wash appliance:

Typical water use/cycle is about 60L= 30cent/cycle.

Plus heating of water to 40degree C =2.8kWh=67cent.

Total: 97cent/wash cycle (€1).

Try to avoid using the washing machine, until it is full.

High temperature water cycle costs much more.

A 90degreeC wash cycle uses about 6kWh = €1.40 + water cost at 30cent = €1.70/wash cycle.

There are much more efficient (low water use & energy) clothes wash appliances available. Choose an Energy label A+++ (and one that is water efficient)

If you wash with ‘night-rate’ electricity meter, it will reduce the cost of heat by more than 50%.

However, ensure you have an effective ‘fire-alarm system’, to protect from fires developing from appliances when left to run unsupervised at nighttime.

5. Kitchen:

a) Appliances: Dish wash appliance:

Water use in dish wash appliance ranges between 18L to 27L/cycle. Say the average is 20L = 10cent/cycle.

Cost of boiling 20L of water =2kWh = 50cent/cycle

(Operating on ‘night rate’ power= 20cent).

Total cost of dish wash cycle = 60cent/cycle

When purchasing appliances, choose an energy/water efficiency rating (Energy Label) A+++.

Try to only use a dish and clothes wash machine when they are full.

b) Sink: The flow rate of a cold-water kitchen tap can vary between 3L/min and 6L/min (This depends on the mains water pressure and the type of tap, mixers etc.)

Washing pots, pans and dishes in sink: – Use a basin in the sink for wash & rinse.

You can reuse the sink wastewater on garden flowers, shrubs and trees.

Wash recyclable containers for green bin with waste water (to save water).

c) Drinking water:

Drinking safe fresh water: Average about 2L/person/day.

Keep a jug (with cover) or glass bottles of cold drinking water in fridge (to avoid wasting tap water, as it adjusts to cool water).

Hot beverages: (Tea/coffee/hot chocolate)=2L/person/day.

To save on heat, only part-fill the kettle with the required amount of water.

Cooking: 3L/person/day

Total drinking water quality used: 5 to 7L/person/day

d) Bottled water:

(35c/L to €1.50/L, 330ml bottle=€3/L= twice the price of petrol).

Bottled water is therefore 70 times to 600 times the cost of tap water (at 0.488cent/L).

Bottled water is usually not any better quality than public water supply.

Plastic bottles make it wasteful in use of resources and energy to produce and transport the bottle. To minimize disposable containers, they need to be recycled.

How many water and beverage drink plastic and glass bottles and beer cans get used in a year? My guess is between 3 and 6 billion are used each year in Ireland.

How much embodied energy and CO2 emissions are generated in their manufacture?

How many of these disposable drinks containers get dumped or create unsightly litter that impacts on nature?

Why don’t we introduce a Deposit-Return on all drinks containers?

As is in most European countries.

15. Average water use/Irish household occupant/day

Bathroom: Shower/bath= 38% (56L). WC flush=27% (40L) & WHB.

Laundry: Clothes wash= 10% (15L).

Kitchen: Drinking 3% (4.5L). Cooking=3% (4.5L). Dish Wash= 7%(10.5L)

Others: (Garden & Car wash) =12% (18L).

6. Cost of heating water:

The heat required to change the temperature of 1kg (1L) of water, 1degreeC = 4.184kilojoule = 1.16Wh of heat.

To boil 1L water in an electric kettle: (to raise from 10degree C to 100degreeC is 90degree C) = 1L x 90 x 1,16Wh =105Wh = 1/10th of a kWh =2.5cent.

The cost of 1L of water =0.5cent.

Total cost (heat + water) = 3cent

7. Fuel price options for domestic heating

Electricity: is very expensive for providing heat. Other fuels can be used. See

Average domestic electricity ‘day-rate’ tariff = 24c/kWh (SEAI -1/7/14)

Oil heating: (Average domestic boiler efficiencies) =12c-17c/kWh.

Natural gas: = 8c- 9c/kWh.

Wood fuel: = 4c-5c/kWh.

Solar: = 0c/kWh ( but there is a capital cost  at the start)

8. Shower water temperature:


Showers can range from a cold/chilled shower to a very hot shower.

Typical minimum comfort temperature of a shower =37degreeC (body temperature) or, a hot maximum =45degreeC (avoid scalding).

Required increase in temperature of say 37degreeC: To calculate temperature change, deduct the average ambient water temperature (10degreeC).

For 37degree C: 37-10= 27degreeC rise.

For 45degree C: 45-10 =35degreeC rise. = 30% more costly

18. Four different examples of showers:

a) Economic (ecological) Shower:

3min (low-pressure shower) at a flow rate of 3L/min = 9L shower at 37degreeC

Cost of 9L water (0.488c/L = about 4.5c

Cost of heating this shower water to 37degreeC

(Electricity tariff at 24c/kWh)

1.16Wh x 9L x 27degreeC=282Wh x24c = 7cent/shower.

Total cost of shower (water + heat) =11.5cent

Cost of taking this type of shower every day for a full year = €42/year

If this type of shower was only every third day, it would be €14/year.

Regarded by medical research for human health:

A shower every three days seems to be healthier than a daily shower, (which removes the important protective bacteria from our skin that are needed to protect from harmful microbes).

b) UK average shower duration= 8.5min.

 Let’s assume it’s a power-shower at a flow rate of 17L/min

 Cost of water: 8.5 x 17L = 144L =72cent.

 Cost of heat: 8.5x 17x 35x1.16=5.9kWh=€1.41.

Total cost (water + heat) =€2.13/shower.

 c) Electric shower: (7.5 -10.5kW output), at 40degreeC

8.5minute shower using a 9.5kw electric shower:

Cost of heating =1.35kWh =32cent

Cost of water =40L = 19cent.

Total cost (water + heat) = 51cent

d) 10min power-shower:

 (Flow rate 17L/min at 45degreeC)

 Cost of Water: 170L x 0.5c =83cent.

  Cost of Heat: 10 x 17 x 35 x 1.16Wh=6.9kWh (say 7kWh)

  = €1.65/shower.

Total cost of shower (water + heat) =€2.48 (say €2.50)

If this extravagant shower is used (indulged) every day, it would amount to a whopping €905/year.

 If a family (2 parents+2teenagers) all took similar long power-showers each day= €3,620/year.

Cost comparison of example A with example D:

Example D costs 18 times example A in water use, and 24 times more in heat and CO2 emissions.

9. CO2 emissions:

Example D:

Electricity used in heating 170L of water =7kWh= 3.5kgCO2.

A similar type of shower taken every day for a year =1.3tonsCO2 =13% of CO2 emissions of the average Irish person used on power, heat and transport, or 40% of total heat.

This does not include the treatment of water supply, pumping water, and wastewater treatment. Example C uses 60m3 of water each year.

This is very excessive! And in my view, quite irresponsible!

We surely cannot continue to indiscriminately dump such massive amounts of carbon dioxide into the atmosphere!

10. Household Garden:

a) Avoid use of a power-hose or sprinkler.

Especially for watering lawns or washing cars.

Lawns can consume massive amounts of water in dry spells, when public water is often in short supply.

b) Grass lawn: Even in drought conditions, grass lawns do not require watering to survive. They may wither in dry spells, but will recover again after rainfall.

Drought-resistant grasses and shrubs can also be selected.

Mow a lawn less frequently during dry spells and allow grass swards to grow higher to provide shade from strong sunlight and to reduce evaporation rate.

c) Fit a ‘water butt’: under the rainwater down pipe.

d) Use a bucket or a watering can: To irrigate flowers and vegetables.

e) Reuse wastewater from kitchen sink: To water trees and flowers.

(Avoid use of soiled water with detergents and grease, for watering fruit and vegetables).

11. Water harvesting:

About 750mm of rain falls each year in the Dublin area. (More rainfall falls in the Western parts of Ireland).

The roof area of an average Irish house is about 100m2.

The average roof in Dublin receives about 75m3 of rainwater per year. About half of this (38m3) can be collected and this is usually divided between the front and rear roofs at about 19m3 each.

The rear roof of an average house can potentially harvest about 20 m3 of this grey-water each year, (saving €90/yr of water). This is assuming that the rainwater storage tank is large enough (say 5m3) to accommodate the periods of heavy rainfall (10mm in 48hours) and there is a constant use for the recovered grey-water (for WC, clothes-wash, showers, garden, etc).

a) Water Butt:

Fitted under the RWP outlet that collects from rear roof slopes. (200litre). Cost €37. What about collecting water from front roof?

b) Fit a rainwater storage tank on flat roofs:

(Then raised height provides a gravity flow to garden level).

c) Install an underground rainwater harvesting & storage system: (There are many systems now available, but they can be expensive).

Need to divert drainage pipes from, gully traps (that rainwater down pipes discharge to) to the underground tank, that’s plumbed to WCs in house. That’s covered, sealed, accessible and fitted with a silt-trap, water-filter and wired for a pressure pump.

d) Provide a decorative/landscaped pond for rainwater storage in the rear garden: -Fence off the pond to protect for children’s safety.

(As kids love water).

12. Housing Estates & Towns:

Provide a large community duck pond in a local public park.

(Made safe for children)

Divert all storm-water with a100mm (or larger size when required) underground drainage pipes laid to the required fall to the pond.

Fit a pump-house and filter system and lay a 50mm polyethylene water supply pipe underground, to connect to a 12mm pipe connection to supply each house.

Amount of rainwater that falls on a roof:

An average house has a roof area of about 100m2.

1mm of rainfall/ m2 = 1litre of water. So 750mm/year= 0.75m3/m2/year

About 750mm of annual rain, falls in the Dublin area (more in the West), each year. This creates 7,500m3 of rainwater/hectare/year, or 750,000m3/km2 that’s spread over the Dublin area.

In extreme rainfall conditions (70-100mm of rainfall can fall in 18 to 24 hours), This huge amount of water, say 75,000m3/km2 that can fall in say 24 hours, can cause extensive flooding.

The use of a large landscaped pond to collect rainfall from all roofs in a housing estate, street or town, including hard-surfaces and roads, will help attenuate heavy ‘pluvial’ rainfall and avoid flooding.

Or, provide large communal water storage tanks, laid above ground or underground, to divert storm water before discharging to existing ‘combined sewers’, found in most older urban areas and towns.

In heavy rain conditions, storm water regularly overwhelms wastewater treatment plants, which regularly contaminates rivers and bathing beaches with E.Coli and Coli forms.

This relatively clean rainwater can be collected and stored in large shallow ponds or underground tanks, before it discharges to combined sewers. It can be used for irrigating plants in public parks and be filtered, pumped and distributed back to the dwellings for grey water uses.

As impacts from Climate Change intensify over the coming years, flood attenuation measures will become essential, but also to store water for use in dry-spells.

13. Cost of heating water in homes:

Shower water:

Power Shower: These rely on a water supply that is boosted by a pump to provide high pressure and a high water flow rate.

They use much more water and energy for heating than the average pressure or low-flow rate showers.

They depend on a large volume of hot water that is already pre-heated in a hot water cylinder. They often are fitted to a powerful pressure pump to boost water flow up to 17L/min (Use 170L in 10minutes).

These pumps can be noisy, vibrate and transmit sound along the plumbing pipe system and through walls.

Electric showers: These depend on electricity to provide pumped pressure to create a desired water flow. (Rather than gravity pressure from a water storage tank or from mains water pressure).

Electric showers range from 7kW to 10.5kW in output.

Most of these showers operate at lower flow rates then power showers and use less water and heat, but they depend on electricity to provide instant heat.

The power consumption of an electric shower is capped at its power output (Most range from 7.5kW and 10.5kW).

Low pressure/low-flow showers: (3L/min).

These usually rely on gravity supply from a water storage tank in attic. They can be economic in their use of water and energy.

14. Calculating the cost of a Power shower

(Say - 10minute shower duration)

- Assume a high water flow rate of 17 L/min, using hot (45degreeC) water temperature that is heated by electricity.

a) Water consumption:

17L x 10min =170 L, charged at 0.5c/L = 85cent

 b) Heat consumption:

To raise 170L of water from 10degreeC to 45degreeC:

  = 170L x 35degreeC x 1.16Wh = 6.9kWh (say 7kWh) x 24cent/kWh = €1.65

 15. Choice of heat sources:

(To heat water at typical efficiency of average heating appliance)

Electric heater or emersion element (day-rate): 24c/kWh.

“Night-rate” meter: 10C/kWh

Oil boiler: 11c-17c/kWh

Natural gas boiler: 8c to 9c/kWh

Wood fuel: wood pellets (in bulk)= 6c to 7c/kWh.

Wood logs/woodchip (in bulk) = 4c/kWh.

Heat-pump: = 5c to 10cent/kWh

Solar heat and electricity (PV) and wind power are free.

16. Fuel options:

–To deliver 7kWh of heat to a shower:

a) 7kWh of heat at a day-rate electricity tariff of 24c/kWh =€1.68.

     Night-rate electricity tariff= 10c/kWh =70cent

b) Oil boiler at 13c/kWh = 91 cent.

Oil boiler Heating by an oil boiler in six warmer months (running at low capacity and at 55% efficiency, will deliver heat at 17c/kWh =€1.19 cent

c) Natural gas (at 9c/kWh) = 63cent.

d) Wood logs in stove at 5c/kWh=35cent

e) Solar, PV and wind power provide free heat

f) Heat delivered by a heat pump: 7kWh = 60c to 37c

 (Average range of C.O.P =1:2.5 (8.5c) to 4:1(5.3c).)

(Heat at ‘night-rate’ electricity by a heat pump = 28c to 21c/kWh).

Day-rate electricity is a very expensive way of heating water (unless by a heat pump).

17. Climate Change and CO2 emissions:

The total CO2 emissions from burning fossil fuel by Ireland’s Residential sector in 2011, was 10.5MtCO2, used in heat and electricity.

The CO2 from energy used by combustible fuel in homes for space heating and water heating amounts to 6.4MtCO2, while household electricity consumption amounts to 4.1MtCO2.

(MtCO2 is  Metric ton of Carbon Dioxide, the main greenhouse gas)

 Irish homes depend on fossil fuel for 97.5% of their heating, where only 2.5% is from renewable sources.

Electricity is expensive for heating, but it is also very carbon intensive, when compared to natural gas. Wood fuel is nearly carbon neutral, while solar creates zero emissions.

 The CO2 emissions/year of the shower used in example (d):

(Power-shower (17L/min) at 45degreeC for 10minutes =7kWh of electricity =3.5kgCO2.

So taking a similar shower for 365 days/year =3.5kg CO2 x 365 =1,277kg CO2=1.28tons CO2/yr.

 If every Irish citizen took a similar ‘extravagant’ shower, this would dump 5.9MtCO2 into Earth’s fragile atmosphere.

(I’ve heard that some people even shower twice a day!)

 This would be equivalent to 56% of Ireland’s total Residential sector’s CO2 emissions (at 10.5MtCO2 in 2011). It would add 5.4MtCO2 to current Residential sector’s CO2 emissions, amounting to 15.9MtCO2/year. A whopping 34% increase!

Just imagine if 50% of the world’s population (3.6billion) showered like (3.5kgCO2) this each day!

= 4.7billion tons of CO2 accumulating each year in the atmosphere.

 However, there are many ways for householders to reduce the massive level of energy and CO2 emissions from this type of shower (by at least 50%).

Water consumption could likewise be reduced by use of ‘aeration’ or a pressure compensating flow device.

 A shower’s CO2 emissions could be reduced to ‘zero’ by heating from solar-thermal collectors, or from electricity that’s generated by PV panels or a wind turbine.

Duncan Stewart,

Earth Horizon Productions




Contact the Show


Call: 01-2083257, 01-2083971, 01-2082339

Text: 51551

Presenter: Dave Fanning


Ways to Listen

Radio Player