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Hundreds of thousands of touring recreational vehicles, caravans and mobile homes, together with pleasure boats of all types and sizes, rely on onboard tanks for personal water supply. There is a correspondingly large number of temporary water users, such as construction sites, camps in remote areas, fishing boats, and so on, all needing a supply of water that is sanitary, and remains so for as long as needed.

Pleasure craft, for example, load a tankful of water from the mains supply at a marina – a source that may also be used for wash-down purposes. Even with the use of a hygienic connecting hose, there is a strong chance that the initial flow from
the source will be contaminated. It is thus recommended that an in-line filter be used in the feed line from the mains to the tank.

Further contamination is then inevitable on standing. Tests conducted with a large plastic container filled with tap water showed an initial bacterial count of 18/ml, which, after only a week, had risen to 45,000/ml. Thus, the equipment commonly
used to store and dispense fresh water in mobile environments leaves much to be desired, unless it is subject to additional treatment. This may range from the simple use of purifying chemicals added to the water, or filtration or a complete water treatment system. Of these, filtration is by far the most attractive of the low cost methods.

In large applications, automatic gravity filters are often used for the treatment of mains or groundwater, including aeration, removal of iron and manganese, and deacidification.

The unit shown in Figure 4.14 is designed to supply sufficient quantities of drinking water in accordance with WHO standards for camps in remote areas, temporary construction sites or hazard areas. The system combines flocculation, chemical feeding and filtration in one unit. Up to 35m3/h of raw water can be treated without the need for the use of pumps, agitators or mixers within the main treatment zone, as

it simply uses the height of the water to provide the driving force. To obtain this hydrostatic head, raw water needs to flow into the reaction tank through a chemical mixing system at a height of 5.6m. The feeding tanks are located 6.6m above the
ground.

The raw water, enriched with flocculant chemicals, flows into the bottom part of the reaction tank, causing an upward spiral current. The settled matter in the form of a sludge is periodically removed from the reaction tank by means of a ring conduit
placed near the bottom of the settling tank. The pre-clarified water then flows down into the automatic gravity filter from the top of the water surface level of the reaction tank. By its own head the water moves down through the filter layer and out to service.

During emergencies the provision of clean portable water from a natural water source is paramount. This sort of plant can be packaged, perhaps into a container ( Figure 4.15 ), and transported anywhere around the world by air, road or sea, and is
used to remove contaminants from a natural water source. Such containerized plant can also be used in a number of applications from short-term emergencies at a water treatment works, to stand-by use when a permanent plant is temporarily shut down.

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