Water Harvesting

General

In the UK, water would appear to be plentiful and well distributed, generally speaking at least.

However, we have all experienced times when drought and other “abnormal” weather patterns have occurred and we suffer such annoying indignities as a hope-pipe ban or flash-floods.

In addition to these annoying inconveniences, the cost of storing this raw material under “normal” circumstances, of ensuring that it is safe to drink and transporting it around the country is extremely high in both financial and energy terms.

When the foul water aspects are also taken into account with the treating of sewage and other foul and polluted discharges from our processing industries, homes and surfaces, water, even in this country, becomes a valuable, and rare, commodity that requires to be preserved and valued just as much as raw energy itself, simply because of its extremely high energy in-use content.

By ensuring the conservation and improved utilisation of water in this country, we shall also develop those techniques that will be needed to be applied in much more water starved areas of the planet and upon which we are becoming much more dependent as time passes.

Water Use

In the UK, water is delivered to most sites, be they commercial, industrial, agricultural, social or domestic in a POTABLE form, ie:- that is fit for human consumption.

However, not all uses within all of the above list requires all water supplied to be fit for human consumption and so, water from non-wholesome sources could in theory be utilised.

It is not necessary, for example, for potable water to be used for irrigating the garden, washing the car and clothes or for flushing toilets.

Sources of non-wholesome water can be various, but would normally include rainwater collection, streams, wells, bore holes and non-foul waste such as bath and shower water, amongst others.

Water Classification

In most countries, water can be classified basically as being in one of three conditions:

Clear:

Wholesome, potable water fit for human consumption and comes from a statutory water supply or from a tested and certified well or borehole.

Can be used for ANY purpose.

Grey:

That clean water derived from fresh rainwater collection methods but not treated, waste from baths, showers and washing-up sinks, chemically inert process waters such as cooling and wash-down waters.

Can ONLY be used for supply to washing machines, toilet cisterns, car wash and garden irrigation purposes.

Black:

This is substantially polluted process water, foul sewage and discharges from washing machines, etc.

Must go to foul sewer and onto treatment works.

Rainwater Harvesting

Rainwater from roofs is collected via a normal down-pipe system and primary vegetation filters into a separate dedicated underground tank which has overflow capability to main sewer, or into above-ground water-butts or a soak-away.

From the underground tanks, where it has been filtered of vegetable matter, it is then pumped on demand, normally via a UV disinfection filter, to points of use such as toilets, washing machine, process cooling and irrigation points, possibly via an intermediate in-building storage cistern.

Grey Water Harvesting

Over a normal yearly cycle, by collecting rainwater as indicated above, some 30% of normal potable household water can be saved.

This saving can be considerably further enhanced if the outlets from such facilities as showers, baths and sinks are also connected into the storage system via suitable grease and particulate filters - this is called GREY-WATER harvesting.

By using such systems, potable water use can be often reduced to greater than 50%, and should heat recovery techniques also be employed when this water is captured even greater energy savings can be achieved.

Stormwater Flood Surge Protection

It is not uncommon for weather incidents to happen where there might be a very sudden downpour and the local main drains cannot cope with the amount on water inundating them. This may cause major local dispersal problems and flash-flooding.

During the construction period, it is possible to construct in the ground-works, flood surge break tanks and networks that will automatically take out a certain designed proportion of the water descending onto that location over that short period and allow it to more slowly discharge into the main drainage system over a longer period of time following the deluge.

There is no reason why this slower discharge cannot also be used as supplementary grey-water systems if suitably filtered, especially if that storage might be used for crops irrigation, process cooling and wash-down waters and the like.

With acknowledgement for use of images to: