Perhaps the most important advantage created by the barrage will be the permanent supply of water for the increasing demands of the London area.

By the Act of 1903 has been created a Water Board which is empowered to purchase the water companies’ properties and to administer them in the public interest. These companies claim £47,000,000 for their properties. The ratepayers pay them £3,000,000 annually for their water, and the companies pay £30,000 annually for the greater part of the water which they draw from the Thames.

The figures are as follows:—

So that two-thirds of London’s water supply comes from the Thames; and as the other sources named above cannot be expanded for future requirements, it is evident that for the increasing demands of London either the Thames or some more distant source must be looked to.

The Royal Commission on the water supply of London estimated that in 1941 these requirements will reach 423 million gallons per day, so that at that date 303 million gallons must be obtained from the Thames or elsewhere.

Now if the Thames is dockised, and the tides kept out of the river, it is evident that much less upland water than is now considered necessary will suffice to keep the river lake fresh and clean, because all sewage and effluents entering the river will be carried directly down to Gravesend; there will be no muddy foreshores and no stirring up of the river mud by the tidal scour.

The river will be, in fact, in exactly the same circumstances as most large lakes—that is, a large body of fresh water, having a main inlet of fresh water at one end, many small inlets along its banks, and one main outlet at its lower end at Gravesend. Such lakes abound all over the world: they are the purest of all waters and never become stagnant.

It is proposed, therefore, that the Thames lake should be regarded as a storage reservoir, so far as water supply is concerned. It will contain sufficient for 320 days’ supply, even at the estimated requirements of 1941; for to whatever extent its waters may become contaminated at and below London, these pollutions cannot work back up the river towards Teddington. It follows, therefore, that between Teddington and London water may safely be drawn off for town supplies, or the supply may be taken as now from above Teddington.

An inspection of the table of flow over Teddington Weir on page 3 will show that in the winter and spring enormous quantities of water, above the quantity considered necessary for scouring the river, flow down and are lost.

A minimum flow of 200 million gallons is fixed by law as the amount needed in summer to keep some sort of cleanliness in the lower river; but in January ten times this amount flows away. It is only for a short time in the months of August or September that the natural flow over Teddington Weir—including the water drawn by the water companies—is a little below 423 million gallons daily, and in those months the surplus might be taken from below the weir without affecting the river materially.

If this be objected to, however, there is another remedy available. The Upper Thames may be used as an aqueduct to convey a larger supply, to be derived from neighbouring watersheds or from wells, the water so obtained to be regulated to meet the requirements, enabling a sufficient amount to be run over the weir to keep the lower river in motion at its upper end. Further down, the small but numerous affluents and springs will keep the river in motion, as they are not affected by the Teddington flow, but give a continuous supply to the river. Mr. Topley, the eminent geologist, in his evidence before the London Water Commission, 1892, stated that there are outside the Thames basin large areas from which water could be obtained, such as East Kent, West Suffolk, Norfolk, Hampshire and Wilts.

It is evident that in this way an enormous prospective outlay for a supplementary water supply for London in the near future may be obviated, and that without adding to the existing plant of the water companies the new Water Board may inherit free of cost a future source of supply which will make their purchase of the London Water Companies’ stocks a good investment and a cheap one for the ratepayers.