Twyford water was hard and it was always intended to provide water softening equipment. Softening had been carried out for many years at Timsbury by mixing milk of lime with the raw water and leaving it in settling tanks for long enough for precipitation of the chalk sludge to take place. With this in view, a mixing or softening tank was provided at Twyford and reported as being completed in 1899, but initially this was used as an auxiliary reservoir. Completion of the softening plant was delayed for nearly three years after the commencement of pumping.

In his report of October 190I. the Consulting Engineer was still contemplating six concrete settling tanks. using the same sedimentation process as that which operated at Timsbury. However. the engineer at the nearby Southampton Corporation Otterbourne Pumping Station had patented a new process which greatly speeded the removal of the chalk sludge by passing the water through filter cloths instead of waiting for the sludge to be precipitated in settling tanks. In December 1901 Baldwin Latham proposed the adoption of Mr Haines' filtering process for Twyford and this was accepted by the Directors. The contracts for the necessary tanks and equipment were let in December 1902. The building work consisted of the provision of a filter house suitable for the Haines patent filters, reached by a subway, and accommodation for the preparation of the milk of lime in a building which would also incorporate lime kilns.The mixing of lime and untreated water would take place in what had been used as an 'open reservoir'. Most of the work was to be carried out by Messrs. F Osman using concrete. The only specified item which, if it was constructed, seems to have not been used for some time was a pipe carrying steam to the filter house for sterilising the filter cloths.

The softening equipment consisted of a lime mill operated by a three throw hydraulic motor and a tank with an agitator for producing the milk of lime. James Simpson and Co. also provided three of Haines patent filters. The elevated position of the lime-making plant, necessitating a rope worked railway for the delivery of chalk and fuel, assisted in the dispersal of the fumes emitted by the kilns. The lime kilns were brought into use, making lime from the chalk excavated from the chalk pit located south of the engine house.

Charging the kilns required skill and arduous labour. The lime burner descended into the kiln and constructed an arch with blocks of chalk over the fire bars. The kiln was then loaded with suitably sized lumps of chalk, and finally the charging door was sealed with bricks and plaster. In addition to stoking the fire, the lime burner had to regulate the temperature of the charge by controlling the flow of air through the kiln. This involved constant attendance for about three days and nights. When burning was complete, the charging door was unsealed by removing the bricks and plaster in the same way as used by brick burners. Digging out the quick lime was an unpleasant task. It was loaded into tubs and carried by the narrow gauge railway to the preparation room. Milling and the addition of water converted it into milk of lime, for addition to raw water in the mixing tank.

Finally, instead of waiting for the resulting chalk sludge to be precipitated, it was filtered out by the Haines patent process. The softened and filtered water was then pumped up to the reservoir which, in the early days, was uncovered. After some discussion, it was decided to deposit the chalk sludge onto land purchased on the north side of the Hazeley Road.

The softening plant was set to work on 8 September 1903. Extensions to the plant were required as the output of the pumping station increased and. in 1905, a contract went to Messrs. J Cochrane for additional filters, the work being completed by the following year. In 1908, bacteriological examination indicated an .output of water not as pure as anticipated. As the water in the wells was pure, it was concluded that there must be a degree of contamination in the softening process. Lime itself was a germicide, so it was decided to cover the mixing tank and to sterilise the filter cloths. (In fact, a steam pipe for sterilising purposes was included in the original contract. But the recommendation in May 1908 to sterilise the filter cloths by 'steaming and boiling' suggests that it may not have been used).

Another problem arose by 1910 when, at peak periods, the flow exceeded the capacity of the mixing tank, and free lime was being carried forward to the filters, with a deleterious effect on the filter cloths. The solution was a lengthening of the mixing tank by 25 feet and, In October 1910. a contract was awarded to Messrs. Playfair and Toole. While the work was being carried out, softening of water was suspended. The Consulting Engineer reported that the extension of the tank was completed by May 1911. By 1917, the demands of the armed services had led to an acute shortage of labour, and Mr Stone gave notice that water softening would cease for the duration of the war. In fact, it was not resumed until May 1922.

As mentioned above, water softening was resumed in 1922, and the capacity of the plant was required to keep pace with the increases in pumping capacity. Towards the end of 1928, the Engineer reported that, as the softening equipment at Twyford could only cope with one and a half million gallons a day, on the occasions when greater quantities were pumped, 'raw' water was added to the station's output. To keep in step with pumping would require three more lime kilns, extra lime storage capacity, and more cylinders and filters in an extended filter house. Following this report, tenders were invited for new lime kilns and an extension to the lime store, and for filters and cylinders in an extended filter house.

In April 1930, it was reported that the brickwork of the kilns was complete, and the roofs over the extended stoking and charging floors were nearing completion. The extension to the filter house was progressing. Finally, in June, the new lime kilns and lime store were in operation, together with the additional filtration plant. There is nothing strange about the extension of the softening plant, and: certainly no surprise in the installation of new filters similar in design to those already giving good service. However, the construction of three new lime kilns, almost indistinguishable from the two earlier kilns, would seem to require explanation. In September 1913, the Southampton Waterworks Engineer, Mr E C Rodda, was asked to report on lime burning at Otterboume. He visited numerous kilns in Britain and France, noting that the cost per ton of lime at Otterboume was over 16 shillings (80p) a ton, compared to about 4 shillings (2Op) a ton at the most efficient French kilns. He concluded that the type of intermittent kiln in use at Otterboume could be improved upon, and requested permission to build a small experimental kiln and also to experiment with the use of chalk sludge from the softening process as a raw material for lime burning. There is no record of these experiments being conducted. By 1929, Mr Rodda was responsible for Twyford and, in view of the above report, it is not clear why he recommended the construction of three intermittent kilns, similar to those already in use at Otterboume and Twyford. The alternatives could have been to supply the lime by outside purchase (as was done after the Second World War) or to install a type of kiln which used less labour.-However, in 1929, the Committee may have been influenced by the reliability and suitability of a well tried design for producing lime of the required quality and, under the economic conditions of the time, disinclined to reduce labour and coal requirements. A suspicion lingers that if the decision had been made three years later, by which time Mr Hawksley had become Waterworks Engineer, it might have been different. In any event, the outcome was three new kilns, to a very traditional design, which were only used for nine years. The extensions were almost indistinguishable in style from the earlier buildings to which they were joined. The next two additions to the treatment plant were ancillary. In 1934, an overhead travelling crane capable of lifting 15 tons was ordered for the filter house. The movement of chalk sludge to the north side of the road was facilitated by the provision of an electric pump supplied by W H Alien and working on the DC supply from the newly installed generator. It was connected by underground pipe to the filters and fed the sludge to two settlement tanks. The pump was housed in a small timber building, which might well have graced a landscape garden.

The last major extension of the softening plant was authorised in 1936, to raise the capacity from 3 million to 5 million gallons a day. This was to be achieved by extra filters and lime cylinders, linked to an extension of the clear water tank. Messrs A E Jukes successfully tendered, for the necessary building extension which, in accordance with Twyford custom, had to be almost indistinguishable from the original building. (The drawings indicate ways in which the brickwork was to be blended in with the existing brickwork). Softening was suspended from 1939 until 1946.

The arrival at Twyford of the diesel engines involved the storage of large quantities of fuel oil, and there was always a danger of small quantities seeping into the water. To guard against this, in 1937, a small plant driven from the water main by a Pelton Wheel was installed in the corner of the lime preparation room. It consisted of a hopper and a mixer for adding small quantities of carbon powder to the water supply. This would absorb oil and the powder would then be removed at the same time as the chalk sludge, by the filtration process. This proved to be a reliable machine but, with the end of the use of diesel pumps and large fuel oil stores, it fell out of use.

Water softening was resumed at Twyford in 1946. However, the lime kilns were not used, as it proved cheaper to bring in lime by road from Derbyshire. The same lime-mixing plant was used, but a new chute was constructed to facilitate the delivery of lime. In 1955, the Waterworks Committee took a decision which might have had serious consequences for preservation at Twyford. In view of the fact that the lime kilns at Otterboume, Timsbury and Twyford were disused, and were unlikely to be used again. it was decided that, unless they were needed for storage space, they should be demolished to provide hardcore. While there was only limited development of either the disinfection or the softening plants, maintenance continued. For instance, in 1960 two new sets of filter plates were purchased from Messrs C J Haines Ltd for £650. For the addition of chlorine, a new chlorinator was purchased for £406 in 1964. The water softening process produced a marketable by-product. The chalk sludge was sold to Messrs Eucryl for use in toothpaste manufacture. In 1967, Eucryls became concerned about the security of their supply and sought reassurance from the Waterworks Committee. They were informed that it was intended to continue water softening, with the consequent production of chalk sludge. for seven years. However, the words 'without prejudice' indicated that this was a declaration of intent and not a contract. Already, at time of peak output, some water was by passing the softening plant, the station could produce five million gallons a day, but the softening plant, with its thirteen Haines filters, had a maximum capacity of four million gallons a day. In view of the increasing use of detergents, the degree of hardness lost significance to the consumer and, in 1969, softening ceased at Twyford. It had been in operation since 1903, with interruptions during both world wars. The preparation plant and the filter house fell out of use, but the large tank in which mixing took place was re-used as a clear water tank. The Haines filters were offered for sale in 1972, and were duly removed and sold. However, all the buildings, with the preparation plant, remained.

In view of our having five lime kilns, we established a co-operative relationship with Bob Bennett who had established a Lime Making Centre near our works.