Utilisation of water

Water is used in every walk of life, but it is frequently wasted or used to less than the best advantage. The purpose of this section is to indicate how water may be saved in each sector.

Agriculture

Without doubt, agriculture is the sector with the highest aggregate consumption of water and significant savings are possible. However, this will often meet with opposition from farmers because of an innate conservatism and resistance to change within the agricultural community. The methods of using water vary greatly according to the nature of the crop.

The secret of efficient use of water is to place it where the plant needs it. A 20 cm long carrot does not need water in the top 5 cm of soil, still less above the soil. Spraying a carrot or potato crop every two or three days is totally useless, because only a very small fraction of the water leaving the irrigation nozzles will eventually reach the level where the plant needs the water. The rest will be unnecessarily lost by evaporation. Worse, if the plant detects water at a higher level than the optimum, it will tend to direct its root system upwards. If the roots are too close to the surface, they will be more vulnerable to damage by the heat from the sun, reducing the health of the plant and making it more susceptible to attack by disease and pests. A healthy plant is one that has a deep root system because it detects the most water below it. In the case of many crops, a good soaking of the soil by surface or, better, sub-surface flooding once every week or ten days is much better than spraying every other day for a comparatively short time.

There are obvious practical difficulties to the above. Where crop rotation is practised, because different crops have different requirements, no permanent installation is possible. The only practical method is to have irrigation pipes between every other row, with trickle nozzles (not sprays) at suitable spacings. The cost of such pipework is relatively high and there is the labour of laying them after each sowing and removing, maintaining and storing them after the product is harvested. An alternative, where it is feasible, is to have the pipes underground, 10 cm deeper than the soil is ever tilled. These can be used after the crop has germinated and the root system has developed to a few centimetres.

Spraying is the most wasteful method of irrigation and should be reserved for only where it is strictly necessary, such as before germination. When it is used, the spray should be adjusted for the largest possible droplet size and the lowest pressure. A fine mist will evaporate up to half the water before it reaches the plant and droplets will remain on leaves where it will evaporate further. With large-leaved plants, such as established cabbages, as little as 10 per cent of the water being sprayed will enter the soil and less than one-quarter of this will be absorbed by the roots. Too high a pressure will cause water to rebound off the soil or plants in the form of a mist, where it will readily evaporate. Spray irrigation should be done in calm weather.

Channel irrigation is better than spraying but is also wasteful because the soil round the channels is also wetted, even where there are no crops to benefit from it. If it is practised, the channels should be cut only where there are crops and the water led to them through pipes, which will also reduce evaporation.

All irrigation should be done in the evening or during the night, so that the water can penetrate to the roots at the coolest time, reducing surface evaporation. The health of the plants will also improve because surface pipework in sunlight will heat the water beyond the desirable limits for the plants. Another advantage is that, although the evaporation will be reduced at night, there will still be some and this may condense as dew on the plants, due to the high local relative humidity, especially if there is not a high wind.

Even experienced farmers can misjudge the amount of moisture in the soil. Simple, cheap, portable, soil moisture meters are available and should be used regularly to the depth of the crop roots to determine when irrigation is necessary. Instruction in the use of these instruments for each crop type is necessary, because each type has different requirements of soil moisture. Better still, a fully automatic system can control the irrigation, in conjunction with a time switch, so that no human intervention is required. This could reliably increase crop yields for a reduced water consumption, at a small extra capital outlay.

As a general rule, the use of water for animal husbandry is difficult to reduce substantially. Animals will drink only the water they need but adequate quantities of clean, fresh drinking water are necessary. When the water is drained from drinking troughs or they are being cleaned out, rather than waste it, it would be better to use it for swilling out stables, byres and pens. This implies a simple collection system.

Industrial Horticulture, Market Gardens and Smallholdings

The same general remarks as applied for agriculture are equally valid in this case. In addition, there are the cases where restricted areas are intensively cultivated, such as in greenhouses, for periods of many years, even decades, frequently with a monoculture or biculture (e.g. tomatoes and cucumbers). This implies the addition of large quantities of nutrients such as natural and chemical fertilisers, as well as water. Much of both the water and the fertilisers drain through to below the plant root level, where they are lost for ever. It is possible to recover about half these wasted fertilisers and water under these conditions, before a new greenhouse is constructed. This is done by excavating the site to a depth of about 1 metre minimum, but with a sloping bottom to the fosse which is then lined with a welded polyethylene 2 mm thick sheet. A collector pipe, with a mesh filter, is fixed close to the lowest point (leave a few centimetres for silt collection) and the excess nutritive water is transported to a storage tank for re-use. Stones should be replaced into the bottom of the pit, followed by the excavated subsoil and then the top soil, before the greenhouse is constructed over it. Water and fertiliser consumption can be significantly reduced. Within the greenhouse, each plant can be trickle irrigated. Because excess water is recovered, it is possible to irrigate at more frequent intervals and with more water than would otherwise be economical. Spraying with clean water is occasionally desirable to remove excess dust from the crop fruit. This is not such a catastrophic waste as in the open, as the evaporated water, along with transpired water from the plant leaves, is more or less retained to raise the relative humidity within the greenhouse and to condense as dew on the plants at night. Even some of this will be recovered. Forced ventilation should not be switched on between the time that spraying is started to the following morning. The extreme theoretical limit to this technique — but not practical, it is emphasised — is to have hermetically sealed "greenhouses" where, once equilibrium has been reached, the only water that needs to be added is equal to that contained in the crops removed from the enclosure (typically 90 per cent of the crop weight).

Market gardeners like to present clean vegetables for sale, as they will fetch higher prices. The housewife prefers to buy clean vegetables, especially root crops. Many producers use flowing water for hand or machine cleaning. Over three-quarters of this water can be recovered for re-use if it is directed to one of two open lined concrete sedimentation tanks of about 2 – 5 tonnes capacity where the silt can settle out. When the silt reaches the level of the exit pipe, the other tank should be put into service, while the silt is shovelled out from the first one. For heavy crops, such as potatoes, the tank capacities may require to be greater and automatic silt removal may be considered.

Industry

The use of water in industry is varied and it is almost impossible to generalise about it. Whole books have been written on the subject as applied to one sector alone. However, it is proposed here to mention a few salient points, illustrated with a few examples. Experts from Protonique SA, including this author, worked in this field for decades.

Without doubt, the largest obstacle to saving water in Cyprus industry is the fact that most of the enterprises are very small and many family businesses are not even registered. They are very frequently under-capitalised and have no resources for installations which will allow water to be recycled. Even those companies which have the financial resources probably could not justify recycling on purely economic grounds. Whether a company is small or large, the capital and running costs of recycling are not very different. The implication is that only industrial enterprises classed as medium or large could, generally, economically justify recycling. However, the equation becomes distorted if waste water quality legislation is very strictly enforced. In this case, the waste water would frequently need to be purified to a degree that recycling may be possible without much extra cost. This could even apply, at times, to small industry.

The five types of pollution in waste water which may require treatment for recycling purposes or for disposal to sewers are the presence of heavy metal or other ions, the correction of acidity or alkalinity, the presence of non-miscible organic materials, the presence of sediments and the presence of poorly-biodegradable dissolved organics.

Without doubt, the most serious type of pollution is the presence of heavy metals. These include relatively benign ones such as tin, but this category also includes the very toxic metals such as arsenic, mercury, lead, antimony, cadmium and many others. Between these extremes, there are moderately toxic metals such as iron, copper and zinc. The presence of these metals are regulated in waste water, but it should be noted that many of them will also halt the bacterial action within septic tanks and sewage treatment works. If water containing these metals is allowed to percolate through permeable rock, some of them may reach water tables which are used for supplying potable water, rendering this water unfit for human consumption. If waste water reaches a dried water bed, dissolved salts will remain, so that the first rains will become so heavily polluted that downstream wild life may be endangered. In addition to metals other similar pollutants such as cyanides, phosphates, nitrates etc should also be removed from waste water.

Heavy metals may enter into water whenever soluble metal salts are present. The most obvious case would be in the rinse water used for cleaning metal parts after electroplating. However, almost any industrial cleaning of metal parts, including electronics assemblies, will pollute water. This includes pickling iron parts before galvanising, removing rust from iron or steel, acidic deoxidation of base metals, removal of brazing or soldering fluxes, and, even to a certain extent, washing cars which will have some metals from the exhaust fumes of other cars adhering to the surface. Similarly, other pollutants may enter into waste water through similar channels.

If the process is electroplating, polymer filtration offers an interesting solution in that the removed metal ions can be recycled back into the original plating bath, at the same time as the water is purified. Apart from the economic advantage, this ensures that there are no waste streams with a more concentrated metal content, producing hazardous waste. Otherwise, ion exchange and reverse osmosis are the most usual ways of reducing metal and other ionic content. Both of these methods produce, sooner or later, concentrated waste streams which are hazardous waste. Precipitation is particularly useful in electroplating applications on a large scale but it produces large quantities of very hazardous sludge which must be recycled to collect the metals; otherwise, they would be dangerous for landfills.

The correction of acidity or alkalinity or, more correctly, the pH is usually done after the removal of other pollutants by the addition of an alkali or an acid until the pH is within the range of 6.0 to 9.0. This can be done entirely automatically. It is usual to monitor the pH of waste water with a strip chart recorder.

Non-miscible organic contaminants fall into two categories: those which are lighter than water, such as oil or petrol, and those which are heavier than water, such as chlorinated or fluorinated solvents. In both cases, they may be removed with the help of a separator whose design must take into account the nature of the pollutant, the speed at which it will separate from the water and the water flow rate.

The method of removing sediments out of waste water will depend on the nature of the pollutant. It is obvious, even to the uninitiated, that a coarse sediment, such as sand, is not the same as a very fine suspended sediment, such as some chemical precipitates. Generally speaking, heavy, coarse sediments will be separated from the water in a settling tank. Finer sediments will require filtration.

Poorly biodegradable pollutants in waste water present difficulties for the bacterial digestion of the water in septic tanks or public sewage treatment systems. If they are present in large quantities, then it may be possible for the digestion to be retarded to such a point that the outflow water will still be considerably polluted and could be dangerous for public health. For this reason, legislative limits must be applied. The method of removal will depend on the nature of the molecule causing the problem. If the molecule itself is very large, such as some soluble polymers, then it may be removed by ultrafiltration. Smaller molecules may be chemically attached to larger molecules which are added to allow ultrafiltration to take place, but this is not universally applicable. Other methods include chemically breaking down the molecule into simpler forms which biodegrade more rapidly or, as a last resort, a large pre-digestion tank will reduce the quantity of poorly biodegradable matter to acceptable amounts.

By combining these methods, it is frequently possible to produce water which is very clean, indeed, and is suitable for recycling. This is of particular interest where the quality of the water required for the process must be very high. In some cases, some useful pollutants may be recovered. For example, in a large hospital with several departments with photographic processes, for record, diagnostic and radiographic purposes, it would be economically justified to pipe the fixer baths to a central treatment unit which would remove the silver and recirculate the treated fixer back to the individual development machines. At the same time, by a similar process, the rinse water would also be treated and sent back to the development machines for recycling. The payback time for such an installation would generally be less than twelve months.

Hotels, Holiday Apartments

It is estimated that about 8,000 to 10,000 tonnes of potable water are consumed daily by hotels situated along the southern coastline of Cyprus, during the high season. These are all situated within reach of a practically infinite amount of water, the sea. Small desalination plants capable of producing a very high quality potable water at a cost of about €1.25 per tonne are available in sizes capable of producing between 50 and 500 tonnes per day. The size of these units is such that they could be placed in the basement of the hotel or in a small prefabricated structure in the hotel grounds. About 40 or 50 strategically placed units could supply the majority of the requirements of the major part of the Cyprus tourist industry, provided that co-ordination between hotels was arranged. Some of the larger hotels could justify their own unit but smaller hotels would have to share a desalination plant between two or three establishments. Obviously, the cost of this water is higher than that which hotels are commonly used to paying but this can be justified when compared with the cost of the water from large desalination plants.

The requirements of the tourist industry are very seasonal and if small desalination plants were scaled to suit the requirements of the high season, a large quantity of surplus water would be produced in the low season. This could be pumped to reservoirs feeding the larger municipalities such as Paphos, Limassol, Larnaka and Ayia Napa. This would reduce the demand on traditional water supplies.

Holiday apartments present a similar situation, in that the demand is largely seasonal, but they have a different infrastructure in that each household is metered separately. If desalinated water from small units was supplied to blocks of holiday apartments, some means of equitable payment would require to be found but this would be best done by the municipalities, as for the traditional water supplies.

In view of the critical situation regarding water supplies, it is suggested that the authorities may consider the installation of such small plants. These could be placed in service within four to six months of ordering, typically one-fifth of the lead time for a major desalination plant, so this is a valid short-term solution. Where such plants are installed by individual hotels on a private basis, consideration may be given to an incentive subsidy and to reduced energy costs in order that the overall costs per tonne of water produced would be comparable to that paid for traditional supplies. Alternatively, the water supplied by the hotel to the municipalities could be purchased at a rate compatible with the same aim.

Regarding the quality of the water supplied by such small units, as has already been stated, this is a high-quality water capable of meeting all standards for both mineral and microorganism content. As this water is being used as potable water either within or outside the hotel, it is essential that the units be fitted with an automatic shutdown system in the event of something going wrong. Most of the units which are commercially available are already equipped with this feature.

Private Habitations

Many of the possibilities for economising water in private habitations have already been evoked. However, it is still very common to find dripping taps and leaky toilet cisterns in houses which are more than a few years old, it is suggested that a major information publicity campaign offering free replacement of tap washers and similar joints could be organised. It would not be surprising if this produced savings of the order of several hundreds of tonnes per day. The capital cost of materials would be very small and a "tiger-team" could go from village to village on a prearranged schedule. At the same time, toilet cisterns could be fitted with volume-reducing bags. The publicity campaign should include television and radio spots, newspaper advertisements and leaflets showing users exactly how much water can be economised without any reduction in the quality of lifestyle. For example, simple acts like shutting off the water during hand washing or teeth-brushing or using a small plastic bowl rather than the kitchen sink for washing salads can all economise water. Above all, baths should be discouraged in favour of showers, wherever possible.

An important saving can be made in many houses because the plumbing systems are operating at low pressures, from roof height, but they are designed for higher pressures. The throughput of water is therefore low. This means that hot water takes a long time to reach some taps. When taking a shower, it reduces wastage to turn on the hot water alone until it starts to run hot and then to adjust the temperature. The shower heads are also dimensioned for higher pressures and volumes. A much more satisfactory shower, using less water, can be had by reducing the number of holes in the shower head by blocking off alternate ones with, for example, a droplet of epoxy cement. The water will flow in a more discrete series of jets and the reduced flow will be compensated by the pressure within the head itself being increased. Special recirculating pumps are available to ensure hot water is instantly available at all times from all taps. Such an installation is expensive (€300-1,000) but a small subsidy is offered by the government to encourage users to install them. Retrofitting to existing houses is possible but may require some external small diameter pipework.

The implementation of grey water systems should also receive considerable publicity so that the private householder could consider them, as well as roof rain capture, the next time that there is a major structural change to the house.

It is felt that the average householder probably wastes between five and 10 per cent of the water he consumes, possibly amounting to an aggregate of well over 5,000 tons of potable water per day.

Private Gardens

This is a thorny problem. Gardens do need considerable quantities of water, averaging a minimum of some 3 tonnes per hectare per day, or about 150-200 litres per day for a medium sized garden, to keep it green. Stopping this completely could be catastrophic. Some persons are dependent on their garden for fruit and vegetables that they could not otherwise afford. Even the most public-spirited person would resent his garden looking like a brown wilderness after he has spent much time building it up from a stony desert. It is therefore necessary for a minimum of water to be available for every garden owner. As already suggested, private well owners should be allocated a volume they can use at no cost and this should never exceed the 3 tonnes per hectare per day scale, pro rata for smaller surfaces, less if the aquifer cannot support such extraction. It is suggested that all village and town municipalities offer transported water for gardens at a cost similar to that for potable water, up to allocated volume. The charge of this could be transferred to private enterprises, if such exist in the region. Any requirements for transported water above the allocated volume would be charged at a commercial rate. This water can be derived from non-potable sources and recycled water or small local dams. This would relieve the pressure on illicit use of valuable potable water.

Any rain captured from house roofs and grey water could be freely used, in addition to transported or well water allocated for the surface. This alone could be sufficient incentive to install roof water collection.

Even thornier is the question of private swimming pools. These often hold 100 to 200 tonnes of water, or more for large ones. In addition, there are considerable losses by evaporation, by drag-out during cleaning and by routine maintenance, typically upwards of 1 tonne/day in very hot, dry, windy weather. In some cases, if they are not kept filled, the linings will deteriorate. Alternate wetting and drying of tiles in full sunlight will cause grouting to fall, increasing the cost of maintenance. There is therefore no cut and dried answer to the problem. Until the crisis shows signs of being resorbed, consideration may be given to some form of fiscal help to swimming-pool owners who volunteer to keep it empty, as compensation for the deterioration that may be expected. Conversely, fiscal discouragement may be charged for those who continue to use a pool. As part of this, the Land Registry may charge an extra fee for all immoveable property that changes hands with a swimming pool. The question of taxing swimming pools has been raised recently in Parliament. At least, these measures would bring the owners’ attention to the problem.

It is suggested that swimming pools be filled and maintained only with transported non-potable water of a quality supplied for gardens, never directly from potable sources, wells or boreholes. This would be an additional sensitisation of the owners towards the fact that water is scarce.

Above all, it should be made mandatory to have a plastic cover over swimming pools at all times when they are not actually in use. This would reduce evaporation. Electrically operate covers are available.