Potable Water Supply to Buildings - Lecture Notes

Potable Water Supply

Introduction

• Potable water is water suitable for drinking.
• The content of this lecture is the subject of exam questions.
• Sample examination questions are included.
• Fail to plan = plan to fail; Succeed to plan = Plan to Succeed.

Acceptable levels of $CO_2$ in a home

• ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) sets standards for recommended indoor $CO_2$ levels.
• ASHRAE suggests keeping indoor levels below 1,000ppm in schools and 800ppm in offices.
  • Background (normal) outdoor air levels: $400 ppm$
  • Typical levels in occupied spaces with good air exchange: $400-1,000 ppm$
  • Levels associated with drowsiness and poor air quality: $1,000-2,000 ppm$
  • Levels associated with headaches, sleepiness, and stagnant air: $2,000-5,000 ppm$
    • Poor concentration, loss of attention, increased heart rate and slight nausea may also be present
  • Exposure may lead to serious oxygen deprivation symptoms:
    >5,000 ppm

Learning Outcomes

• Water Sources “abstraction”
• Typical Water Treatment
• Water Distribution
• Rural Water Supply and Group Water Schemes
• Domestic Water Supply and TGD G Hygiene (July 2011 edition)
• Stop cocks
• Metering
• Cold potable water supply to a domestic dwelling at ground level - details

Water Sources

• Abstraction is the word used for sourcing the “raw” water which we treat.
• Principle sources:
  • Surface water sources, i.e. rivers and large lakes
  • Boreholes into aquifers (water bearing strata, ground water)
  • Rooves, paved areas and shallow wells
• A fourth possibility is the desalination of sea water but this is energy intensive, expensive.
• Waste water can be purified and recycled as a last resort.
• The majority of treated potable water is sourced from natural or manmade clear water reservoirs.
• These are often high above sea level, to take advantage of the gravity flow of water through the treatment and distribution system wherever possible.

Man-made reservoirs

• Manmade reservoirs can be contained within clay-lined earth embankments, (puddling clay) or can be constructed by the flooding of naturally occurring valleys (which may also be harvested for hydroelectricity via a dam).

Surface water

• Surface water can be sourced from local lakes, rivers, and streams, (80%) and natural springs (Water that is naturally seeping from of the surface of the earth, where impermeable bed rock or clay layers of earth meet the surface, (approximately 7%).
• Alternatively it can be sourced from wells or boreholes into aquifers (water bearing strata) (11%).
• Or from rooves, paved areas ($2\%$ from rainwater collection) and shallow wells. (Rainwater harvesting lecture, later)
• The first two categories lend themselves to subsequent filtration and chemical treatment, before distribution and consumption.
• The latter category could be contaminated and are only used in remote locations.
• It is not common practice to use run-off in urban areas for any potable water supply.
• If it were proposed in a remote location, a processing plant would be required to ensure drinking water quality, which is often not cost effective.

Ground Water Sources

• Wells, boreholes

Water Treatment

• Depending on the water quality at the source, different treatment systems (“regimes”) are designed to bring the water up to potable water standards.
• These are continuously monitored in accordance with EU Directives and Irish legislation e.g. EU Drinking Water Regulations (2000)

Typical Parameters / Contaminants

• Colour
• Odour
• Taste
• Turbidity
• pH neutral
• Chlorine
• Fluoride
• Faecal coliforms
• Cryptospiridium
• Aluminium
• Trihalomethanes
• Chloroform
• Iron
• Ammonium
• Nitrates
• Nitrites
• Heavy metals
• Manganese

Water Purification

• Water purification is the process of removing contaminants from a raw water source.
• The goal is to produce water for a specific purpose with a treatment profile designed to limit the inclusion of certain specific materials; most water is purified for human consumption i.e. drinking water or potable water.
• Potable water is drinking quality water. It should be ‘colourless, clear, odourless and pleasant to taste’

Impurities

• Settleable solids
• Suspended solids
• Dissolved salts
• Germs bacteria viruses cryptosporidium etc.

Methods of Water Treatment

• Storage: settlement and clarification.
• Filtration: slow sand filters, rapid sand filters, micro-strainers, membrane filters (RO) et c..
• Disinfection: chlorination and ozonation ($O_3$), UV light, etc.
• Alternatively, it could be described as at seven-stage process…

Seven-stage process:

• Stage 1: Intake - Water is sourced from surface supplies (e.g. lakes and rivers).
• Stage 1: Intake - Water is sourced from underground sources (e.g. wells). As the water travels below ground it is naturally filtered.
• Stage 2: Screening - The water is passed through a fine wire mesh to remove debris, such as twigs and plants etc.
• Stage 3: Settling - The water is moved into large settling/sedimentation tanks. Whilst in the sedimentation tank the water is treated with a chemical known as 'Alum' (aluminium potassium sulphate) to remove any cloudiness or discolouration.
  *Note: Fluoridation takes place in Republic of Ireland; not general practice in EU

Sedimentation

• Sedimentation is the gradual sinking of solid impurities that are suspended in the water.

Clarification

• Clarification is a system of chemically assisted sedimentation used for the removal of very fine suspended particles that do not settle naturally.
• A chemical such as aluminium sulphate (alum) produces a precipitate when it is added to the water.

Filtration

• When water is passed through a fine material such as sand or a wire mesh, particles are removed from the water.
• Some filters, such as rapid sand filters, act only as a simple physical filter and the water also requires chemical treatment.
• Slow sand filters, however, combine a physical action with a biochemical and a biological action.

Slow sand filters

• Slow sand filters are built in sunken rectangular basins, with $100m \times 40m$ being a typical size.
• The floor of the filter bed contains a system of collector pipes and underdrains covered with a layer of graded gravel.
• Above the gravel is a layer of sand, about $600 mm$ deep, which is then covered with water to a depth of around 1m.
• Water slowly percolates downwards through the sand bed which develops a film of fine particles, micro- organisms, and microscopic plant life.
• It is this complex ‘vital’ (living) layer which purifies the water by both physical and biological action.
• Because the growth of the active film reduces the rate of filtration, the head of water is gradually increased until, after a period of weeks, the bed has to be cleaned.
• A clean filter is then ‘charged’ by slowly filling it with water from the bottom upwards and then allowing a new vital layer to form.
• The slow sand filter is extremely effective and gives high-quality water, which needs little further treatment.
• These filters, however, occupy larger areas and work more slowly than other types of filter.
• Compressed air back-wash to clean the filter.

Disinfection

• Chlorination / Ozone
  • Chlorine is an oxidising agent that kills organic bacteria cells.
  • Kept liquefied in tanks and injected into the water at a controlled rate. (dosing).
  • Ozone ($O_3$) is a form of oxygen with molecules that contain an extra atom making it reactive and excellent at sanitising water.
  • It has a higher cost associated with it and is more specialised than chlorination.
• U.V. Reactors
  • In nature, the sun produces UV rays which have a germicidal effect on disease causing pathogens in water.
  • When these contaminants are exposed to UV light, they are rendered harmless and the output water is considered disinfected.
  • An adequate UV dose to kill the following contaminants among many others:
    • E. coli
    • Salmonella
    • Legionella Pneumophilia
    • Mycobacterium Tuberculosis
    • Poliovirus
    • Hepatitis
    • Cholera
    • Streptococcus
    • Corona Virus COVID 19
    • CRYPTOSPIRIDIUM (not killed by Chlorine, resistant)

Additional Treatment

• Many industrial processes require water with lower mineral content than is acceptable for drinking water and further treatment stages, such as softening, are then necessary.
• The addition of chemical compounds containing metals such as copper and aluminium needs to carefully monitored and controlled.

Alternative Water Treatment Approach

• Rapid gravity granular activated carbon filters.

Waste and Discharge from Water Treatment Plant

• Waste discharge from water treatment plant is governed by EU directives and Irish legislation.

Water Distribution

• Water distribution networks: a series of high volume, high pressure (?) pipelines which decrease in size towards every dwelling, industrial and commercial property, wherever possible.
• They utilise gravity feed, pumped feed or gravity-induced via water towers locally, close to high volume distribution centres in low-lying towns or cities.

Rural Water Supply and Group Water Schemes

• Rural water supply outside of town and city distribution networks is supplied through group water schemes in Ireland (approximately 8%)
• A community based initiative, generally supported by government grant aid
• Water supply is part-privatised

Funding model

• The previous funding model is no longer sustainable
• It is costing €1.2 billion every year to run the public water system, with €1 billion of this funding coming from the Exchequer.

Water Metering

• Water meter: measures the amount of water supplied to your building.
• Meters are placed in a meter box, which are be fitted underground on public land. These meters feature Automated Meter Reading (AMR) technology.
• These Meters can be read by a 'drive by' method rather than by an individual visit by a human meter reader.
• This means we won't need to enter your property to take a reading and we can read them more efficiently.
• AMR meters also provide information about the household's water usage so we are able to show you how much water you have used.
• By knowing a bit more about how much you use it will hopefully make it easier to manage your water usage better.
• In August 2013, Irish Water (now Uisce Éireann) began the process of installing water meters countrywide.
• The majority of households have had a meter fitted by 2017.
• There is no need to apply to have a water meter installed.
• At least 14 days before the work begins you will receive an information pack that explains our work, and what to expect when we install your water meter.
• The installation may take up to two hours and disruption will be kept to a minimum.
• There is no direct charge for the fitting of a water meter.

Leaks in the Distribution System

• It is estimated that from 33% to 50% of treated water is lost due to leaks in the distribution pipes.
• 150 litres of water per day is treated for every user
• 90 litres of this water gets to the user. (60%)

Water Charges and Metering

• Note: even if water charges are not applied, metering is still useful.
• Metering helps provide information leading to the detection of leaks in the system.

Water Meters

• It is a standard condition of planning permission that the water supply details, including metering, shall be agreed with the water supply authority, i.e. Uisce Éireann.
• Installation of a water meter is done by Irish Water Uisce Éireann

Domestic Water Supply

Irish building Regulations

• www.environ.ie
• Click here for TGD part G
• The Technical Documents, commonly known as TGD's give guidance on how to construct a building so that it complies with the Regulations.
• Where works are carried out in accordance with the TGDs, this will indicate compliance with the Regulations.
• The adoption of an approach different from the TGD's is not prohibited, provided that the approach meets the requirements of the Regulations.

Assignment

• Go to www.environ.ie/en/TGD and download:
• Building Regulations TGD (Technical Guidance Document) Part G "Hygiene“ (“reprint July 2011” edition)
• Print out and bind pages NUMBERED 5, 6, 7 & 8 of TGD pt G
• Bring them into every class for the next while.

Stop valve

• All water mains distribution pipework is subject to pressure. Flow can be shut off locally through the use of a stop valve.
• The stop valve provides an easy shut-off to a dwelling.
• Typically found underneath the kitchen sink.

TGD G, Hygiene

1.9.1

• The underground service pipe from the external meter/stopcock to the dwelling has a minimum cover of 600 mm.
• The minimum cover should be maintained along the whole pipe length.
• Where the pipe is close to the external wall, the pipe should be insulated with insulation impermeable to water vapour (see Diagrams 1 & 2).

Table 1

Minimum insulation thickness (mm) to protect against freezing for domestic cold water systems (12 hour period)

• Initial water temperature: +2°C
• Minimum ambient temperature: -6°C
• Permitted ice formation: 50%
• Evaluation period: 12 hours.

Assignment (Architectural Technology Students)

• Draw a neat, annotated diagram of the cold water feed from a distribution pipe into a dwelling (40%)
• Include a water meter (10%)
• Make allowance for the requirements under TGD G Hygiene, assuming a floor condition as illustrated in Diagram 1 (30%)
• Ensure a neat, clear illustration, well centred on the page (10%)
• Use adequate annotation for your drawing (10%)

Review

• Water Sources "abstraction"
• Typical Water Treatment
• Water Distribution
• Rural Water Supply and Group Water Schemes
• Domestic Water Supply and TGD G Hygiene (July 2011 reprint)
• Stop cocks
• Metering
• Mains (potable) water supply into a domestic dwelling at ground level - details

Student Exercise

• In groups of 2-3 people, research manufacturers and sizes of cold water cisterns
• e.g. typical flat 340 litre domestic cold water cistern
• e.g. typical upright 340 litre domestic cold water cistern

Sample exam question

• Question : WATER SERVICES
  • (a) Discuss the abstraction, processing and distribution of a municipal mains water supply by the Water Authority (Uisce Éireann). (12 marks)