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RAINWATER HARVESTING. DOES IT HAVE A FUTURE?. S E WIELEBSKI MSc (Dist) CEnv PEng FCIOB FBEng MSPE ACIArb FRSA DIVISIONAL DEVELOPMENT DIRECTOR. RAINWATER HARVESTING DOES IT HAVE A FUTURE?. A few thoughts to set the scene A little bit of history A review of RWH from a Developers perspective

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Rainwater harvesting

RAINWATER HARVESTING

DOES IT HAVE A FUTURE?

S E WIELEBSKI MSc (Dist) CEnv PEng FCIOB FBEng MSPE ACIArb FRSA

DIVISIONAL DEVELOPMENT DIRECTOR


Rainwater harvesting does it have a future
RAINWATER HARVESTINGDOES IT HAVE A FUTURE?

  • A few thoughts to set the scene

  • A little bit of history

  • A review of RWH from a Developers perspective

  • Flood & Water Management Act 2010/CfSH’s implications

  • Potential impact on new home owners

  • Decision time


Rainwater harvesting1
RAINWATER HARVESTING

  • A few questions to get you thinking about the wider picture:

    • Is it just a fad or an effective means of responding to the climate change agenda?

    • Does it make an effective contribution in terms of flood risk mitigation?

    • Is it affordable?

    • Consider the present Government’s approach to new guidance and regulation, i.e. one in one out with any new requirement being cost neutral to industry, therefore……

    • Given the (additional) capex cost of RWH what do we say has to give way to pay for it?

    • Wider implications arising from the FWMA 2010

    • Impact on the zero carbon agenda


Rainwater harvesting uk water companies
RAINWATER HARVESTINGUK WATER COMPANIES

  • Based on Water Company statutory leakage returns to Ofwat

  • If Water Companies reduced their leakage by 1% it would…..

  • Provide sufficient potable water to serve…….

  • 160,000 new homes


A few more wasc facts
A FEW MORE WaSC FACTS

  • Water Companies – little if any investment in new infrastructure since privatisation; in urban areas, several reservoirs decommissioned and sold for residential development

  • House-builders have contributed circa £1.25 billion in infrastructure charges since WIA 1991; rationale – additional water supply and sewerage infrastructure provision to meet the needs of a plan-led planning system

  • Current combined infrastructure charge - £600/dwelling (before the recession this provided WaSC’s with an annual income of around £100 million)

  • Pollution from agriculture is degrading water resources so severely that some have had to be decommissioned


Rainwater harvesting2
RAINWATER HARVESTING

  • Does it make an effective contribution in terms of flood risk mitigation?

  • In short, no because………

    • The Environment Agency do not recognise it as an effective means of surface water run-off volume control, which means…..

    • Tank full conditions must be allowed for, therefore no corresponding reduction in SW infrastructure cost


Rainwater harvesting3
RAINWATER HARVESTING

  • Is it affordable?

  • Miller Homes experience - £2500 to £3000/dwelling in terms of additional cost (excluding soil disposal cost)

  • Note - there is little difference in cost even if we consider communal RWH systems

  • At a plotting density of 17 dwellings/acre (PPS3) = ave £46,750/acre in terms of compensating land value but……..

  • This cost has to complete with others arising from an increasing regulatory burden

  • So what do we do without to pay for it?



Secondary issues
SECONDARY ISSUES

  • Variable rainfall intensities across the UK – SE lower rainfall

  • Additional energy costs not factored into the regulated energy use of a new home – issue with carbon compliance (zero carbon strategy)

  • Outcome of NHBC Foundation research: RWH = additional carbon emissions therefore, not truly sustainable

  • Installation in contaminated ground – impact on a approved remediation strategy not fully considered and/or appreciated.

  • CDM Regulations & Health and Safety


Impact on remediation
IMPACT ON REMEDIATION

  • 80% of approved remediation schemes for contaminated land rely on inert cap and cover systems – most sustainable & cost effective approach (relict contaminants allowed to remain in-situ)

  • The installation of underground RWH storage tanks:-

    • re-introduces the pollutant linkage

    • results in more contaminated soil arisings having to be disposed of to licensed landfill – contrary to current Government landfill disposal policy.

    • increases the cost of remediation

  • Typical soil disposal costs for a 2000 litre tank:-

    • Inert soil – c£145

    • Non-hazardous soil – c£720 (nominally elevated contaminants)

    • Hazardous soils – c£1440


Rwh tanks above ground
RWH TANKS ABOVE GROUND

  • A real issue for a number of planning authorities

  • Reduces garden amenity space and therefore is a sales disincentive

  • Tanks susceptible freezing

  • In winter conditions some would advocate emptying the tank and decommissioning the pump to prevent frost damage


Design implications
DESIGN IMPLICATIONS

  • Competition for space with SuDS – in particular soakaways/infiltration cells/swales

  • Landscaping – position and type will be affected

  • Limit of approach to foundations needs careful consideration - must not adversely affect foundation construction/cost

  • Location of RWH tanks both above and below ground with be affected by the introduction of the forthcoming Mandatory Build Standards (MBS) for adoptable sewers. With effect from the 1st October 2011, this will include all domestic drainage (in gardens) serving two or more dwellings

  • Communal systems – easements for distribution pipe-work



Health safety issues
HEALTH & SAFETY ISSUES

  • We can deal with the water quality side of things – biocides etc but…

  • How do we future proof plumbing installations against RWH being de-commissioned and a return to the use of potable water?

  • On a similar note how do we stop ‘tampering’ with the system thereby increasing the risk of cross contamination? (Recent incident in Anglian Water, E-Coli infections)

  • As a designer, what are my legal obligations under CDM Regulations?

  • As a designer, do I have legal responsibility for latent issues arising from uncontrolled modifications to a RWH system? DIY implications


Additional considerations
ADDITIONAL CONSIDERATIONS

  • Limited rainfall - longer detention times – increased degradation in water quality – greater propensity for compromised public health

  • Back-up required from potable water supply – waste of resource and energy

  • Regular maintenance required to maintain efficiency and effectiveness

  • Additional house-holder cost – routine and annual maintenance – therefore sales disincentive

  • Geotechnical considerations – increasing reliance on SuDS infiltration – latent changes in groundwater regime – mitigation of floatation effects may have to become routine


Decision time
DECISION TIME

  • Principle of RWH – accepted

  • Engineering principle – work from the whole to the part not the reverse

  • Surface water management – start at the ‘macro’ level, design the most effective solutions following the SUDS train management concept

  • RWH should be the very last resort

  • A message for Water Companies – Part G current water usage 125litres/person/day, why continue to base water demand for new supplies on 150 litres/person/day + an allowance for leakage?


Rainwater harvesting4
RAINWATER HARVESTING

  • From a developers perspective – it is not cost effective

  • When considered alongside other legislative changes that will be introduced by Government under the FWMA 2010 – RWH low on the agenda

  • From a personal perspective, as a designer I have serious concerns about the longer-term implications – currently no control over what home-owners can do with their plumbing systems. What are my liabilities under CDM?

  • Duty of care implications


Rainwater harvesting peer review conclusions
RAINWATER HARVESTINGPEER REVIEW CONCLUSIONS

  • “ROI is unfavourable given the high installation costs and current relatively low price of mains water” – DCLG Report BD 2833 December 2010

  • High capex cost, running cost, and carbon footprint do not meet the test of sustainable construction – NHBC/BRE Foundation Research 2010

  • SuDS Standards will replace CfSH’s SUR 1 category from April 2012

  • Take due cognisance of the unintended consequences – HBF 2010/2011



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