Globally, water scarcity is as important as energy, and has an impact on health, and food production. A large proportion of the worlds population do not have access to safe water.
In the UK, we are assured a relatively secured supply of water. However, changes in the climate could result in more rain but not necessarily in the right place. Globally, we may see some areas getting wetter, while others becoming even hotter and drier resulting in a larger disparity between continents.
In the UK, around 1 in 6 properties are at risk of flooding. These increased flood risks are due to the reduction in permeable surfaces from increased building on new land. More run off from hard surfaces and increased rainfall due to climate change also contribute to high flood risk.
As the climate continues to change, we can expect flooding to affect more people, particularly those living in coastal areas, near rivers and in the south.
There are four flood zones associated with risk of flooding. Zone 1 is the lowest risk area, and zone 3b the most high risk to flooding.
A detailed feasibility study should be carried out early on in the planning stages to establish flood risk and suitability to build. There are many resources available to aid this type of study, a good starting point being the Environment Agency [www.environment-agency.gov.uk/flood].
Developments should only be built in areas with a low flood risk. Some questions in relation to flooding to consider when planning a new building.
Water run off is usually diverted to the storm water sewers. During periods of heavy rain these sewers can become overloaded and flooding occurs. The increased water run off is in part due to increased impermeable surfaces in urban areas, as well as a changing climate.
A sustainable urban drainage system (SUDS) allows more water to be absorbed naturally during periods of heavy rainfall and essentially acts as a sponge for surplus water. This reduces the demand on sewers to carry the water away, and reduces potential flooding. A SUDS system will also allow the local water table to replenish. The SUDS method is simple, using porous paving, avoiding impermeable materials, using soft ground cover, increasing landscaping and planting, channeling water to filter naturally into the ground rather than to drains.
There are many different types of SUDS systems briefly outlined below:
Approximately 150 litres of water are used per person, per day. Typical water uses are explained in the table below:
People in the UK are consuming more water than every before. There are many strategies that can be implemented to conserve water, some of which are very simple, others can be costly and more difficult to install. The main principles of water conservation are:
- harvest renewable or local sources
- reduce usage
- reuse primary supplies where possible
- recycle wastes
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Simple methods of reducing overall water use in buildings include tackling toilet flushing which accounts for 30% of overall usage. This can be reduced by 50% or more by installing dual flush WCs. A typical WC uses 9 litres of water per flush, while a dual flush or low flush system will only use between 2.5 and 4 litres.
An average bath uses 80 litres of water, whereas a shower can reduce both water use and CO2 emissions by 65%. Power showers use considerably more water than a standard shower.
Key points for reducing water usage:
- Always choose water efficient appliances and installations
- Select smaller baths with a lower water capacity
- Avoid specifying power showers
- Avoid specifying electric showers as they have a higher CO2 emission than standard showers
- Look for A+ rated appliances
- Consider the CO2 emissions alongside the water saving potential
- Specify water saving taps
- Specify automatic shut off in commercial buildings
Around 150 litres of waste water is produced per person per day. Just as the toilet is responsible for the majority of water usage, it is also responsible for the majority of waste water. An average household produces 40m3 of black water or foul water per year.
Foul water is usually flushed away into the sewers for treatment at a sewerage plant. However, it is possible to recycle foul water on site. Foul water treatment must always be designed by a specialist according to specific project requirements. Some foul water recycling options can be costly and are not always suitable for the site, however, some of the options are listed below.
- Compost toilet – a waterless toilet that allows the natural process of waste into compost (not suitable for urban or public buildings)
- Holding tanks – a septic tank that gradually separates the solids from the waste water so it can be treated.
- Living machine – this is a natural process where vegetation is placed on hydroponic tanks that treat and recycle the wastewater. It is quite costly and not widely used at the moment.
- Reedbeds – these systems treat and recycle wastewater through natural processes using a biological ground system. Not suitable for urban areas.
Often the above options are selected due to remote locations where connection to a mains sewerage system is difficult.
Grey water (which can be described as water from households including shower, bath, bathroom sink, washing machine – not kitchen or toilet waste) can be reused by processing it into usable water for toilet flushing, watering and cleaning purposes.
Grey water must be used immediately after recycling to prevent bacteria build up, or it must be chemically treated. Grey water recycling systems must be considered carefully, as they can create more CO2 emissions from pumping and cleaning than using water directly from the mains supply. Some recycling strategies include:
- Short retention system – a direct collection from the shower or bath and basin, which is fed to cisterns for flushing
- Reedbed – this requires large areas and only suitable for rural areas. Water passes through a UV light prior in order to kill any bacteria. Suffers some water loss through evaporation.
- Biomechanical systems – uses bacteria to break down organic matter in an enclosed system.
It is always preferable to reduce water use over recycling waste water.
Rainwater harvesting can reduce the consumption of drinking water by half. Rainwater is suitable for use for flushing, washing and cleaning and for watering the garden. Harvesting rainwater can also reduce the load on the wastewater systems.
In the UK, a storage tank of around 200,000 litres is required to meet the expected demand over a year. A simple filter and pump can allow the water to be used for flushing toilets, washing machines, garden irrigation and showers and baths. Rainwater is harvested from the roof and stored in a tank located in the ground or basement. In larger buildings this system is also possible, on a larger scale.
Detailed design calculations will need to be carried out to predict rainfall, runoff coefficient and tank storage size along with pump requirements. Some problems do exist with the rainwater harvesting system. These include:
- Storage space for water tanks can be limited. New build construction can design this into the scheme but in existing buildings the weight of stored water can make the option prohibitive.
- Quality of rainwater can vary according to area and treatment and generally will not be suitable for drinking
- Initial construction costs to implement a rainwater harvesting strategy can be costly and capital may not be recovered quickly.
- The building will need to be designed to maximise water catchment, which could have an aesthetic consequence.
Appreciating our water
97.5% of the earth’s water is saltwater. If we were to put the worlds water in a bucket, only one teaspoonful would be drinkable.
In the world, 2.5 billion people do not have access to adequate sanitation, that is almost two fifths of the world population.
1.4 million children die every year from diarrhoea caused by unclean water and poor sanitation.
In the UK we are extremely lucky to have unlimited access to clean and safe drinking water and sanitation.