ferent seasons of the year, depending on the length of contact. Many New England surface waters are highly colored and have the appearance of weak tea (the "meadow tea" of Thoreau). Color can be removed by chemical treatment and filtration and to a certain extent by storage and exposure to sunlight. Odor and taste are closely allied, both conditions usually being present in the same water. Odor in water may be caused by vege table matter, microscopic organisms, or chemicals in solution. Many waters that are highly colored have a distinct odor of humus or musty wood, derived from the vegetable matter with which they have been in contact. Microscopic organisms are a prolific source of a variety of odors, many of which are highly objectionable. Such odors are caused by oily substances generated by certain growing organisms and hence vary with the concentration of these organisms at different seasons of the year. They are most noticeable in stored waters exposed to light and air. These organisms on decaying give rise to still other kinds of odors and tastes that are mostly disagreeable. Certain chemicals may also produce marked tastes and odors, such as the paint of new water pipes or waste coal-tar derivatives from gas works and allied industries. Excessive dosage of water with chlorine gas or hypochlorite of lime also produces marked tastes at times. Turbidity of water is caused by opaque substances held either in suspension or colloidal solution. Turbidity may be caused by clay, silt, iron, microorganisms, organic matter, etc., and is generally more pronounced in surface waters. Underground waters as a rule are clear, with little or no turbidity. Excessive turbidity is most common in waters draining from clay soils and settles out more slowly when in this form. Turbidity can be reduced by sedimentation and storage and can be entirely removed by coagulation with chemicals, followed by filtration. Temperature of water is of necesssity a varying factor, depending on season, latitude, and source. The temperature of surface waters fluctuates between much wider limits than that of ground waters, and for this reason the latter are generally preferred, if available, especially in warmer climates. Whipple states (1, p. 28) that when the temperature of water exceeds 60° F. it becomes unpleasant for drinking. and he further assumes that half the consumers would object to a temperature exceeding 66°, and all would object to a temperature of over 75° F. Another result of higher temperatures is an increase of microscopic organisms and plant life, with the consequent probability of increased tastes and odors. Possibility of Pollution. The potential dangers and possibilities of pollution of any source of water supply should be thoroughly investigated and analyzed because of the direct bearing this group of factors has on the develop ment of the source. Any community is usually limited to a comparatively few available sources of water supply, and the selection of any source must take into consideration the factors enumerated under this head, if not from the standpoint of acceptance or rejection, then from the standpoint of nature and degree of treatment necessary to counteract the effects of such pollution factors as are found to exist. Some of the factors requiring consideration under this head are geological formations of the area, surface scour and wash, vegetable and animal growths, and contamination by human agencies. The geolical formation of any area has much to do with the possibilities of pollution of water supplies. A tight clay soil offers much less probability of wastes from a pit privy percolating to a near by well than would a coarse gravel stratum. Fine, porous, sandy soils also act as natural filters and reduce the potential danger of pollution. On the other hand, cavernous limestone regions containing free underground channels where polluting wastes may be carried for long distances are highly dangerous. In fact the sewage from some cities in such regions is sometimes discharged into sinks with unknown outlets. Many instances are on record where peculiar geological formations have been the direct cause of serious epidemics of water-borne diseases. Knowledge of the geological formation is also of value from the standpoint of mineral pollution of possible water-supply sources. Thus the underground waters of certain areas are strongly impregnated with sulphur, rendering such waters useless as sources of supply; other areas produce only highly saline waters, and still others have an abnormally high iron content. Even surface waters may be seriously affected by contamination with highly acid drainage from active or abandoned coal mines, or may be liable to be so contaminated if coal measures form a part of the geological strata. Surface wash also, plays a part as an active or potential source of pollution. High turbidities are mostly the effect of excessive surface scour, which brings to the stream a conglomerate mixture of polluting substances, including dangerous and offensive organic matter deposited on the watershed. Usually such pollution is highest at periods of high-stream flow, regardless of the increased dilution at such times. Flashy, quick-spilling streams with wide and sudden variations in discharge need, therefore, to be carefully examined when considered as sources of supply. Forestation is usually conceded to have a deterrent action on soil erosion, and is therefore of value in the protection of watersheds, hence in the reduction of turbidity of streams. Vegetable and organic growths also play a part in the possible pollution of water supplies. Water coming from some sources may ferent seasons of the year, depending on the length of contact. Many New England surface waters are highly colored and have the appearance of weak tea (the "meadow tea" of Thoreau). Color can be removed by chemical treatment and filtration and to a certain extent by storage and exposure to sunlight. Odor and taste are closely allied, both conditions usually being present in the same water. Odor in water may be caused by vege table matter, microscopic organisms, or chemicals in solution. Many waters that are highly colored have a distinct odor of humus or musty wood, derived from the vegetable matter with which they have been in contact. Microscopic organisms are a prolific source of a variety of odors, many of which are highly objectionable. Such odors are caused by oily substances generated by certain growing organisms and hence vary with the concentration of these organisms at different seasons of the year. They are most noticeable in stored waters exposed to light and air. These organisms on decaying give rise to still other kinds of odors and tastes that are mostly disagreeable. Certain chemicals may also produce marked tastes and odors, such as the paint of new water pipes or waste coal-tar derivatives from gas works and allied industries. Excessive dosage of water with chlorine gas or hypochlorite of lime also produces marked tastes at times. Turbidity of water is caused by opaque substances held either in suspension or colloidal solution. Turbidity may be caused by clay. silt, iron, microorganisms, organic matter, etc., and is generally more pronounced in surface waters. Underground waters as a rule are clear, with little or no turbidity. Excessive turbidity is most common in waters draining from clay soils and settles out more slowly when in this form. Turbidity can be reduced by sedimentation and storage and can be entirely removed by coagulation with chemicals. followed by filtration. Temperature of water is of necesssity a varying factor, depending on season, latitude, and source. The temperature of surface waters fluctuates between much wider limits than that of ground waters, and for this reason the latter are generally preferred, if available, especially in warmer climates. Whipple states (1, p. 28) that when the temperature of water exceeds 60° F. it becomes unpleasant for drinking, and he further assumes that half the consumers would object to a temperature exceeding 66°, and all would object to a temperature of over 75° F. Another result of higher temperatures is an increase of microscopic organisms and plant life, with the consequent probability of increased tastes and odors. Possibility of Pollution. The potential dangers and possibilities of pollution of any source of water supply should be thoroughly investigated and analyzed because of the direct bearing this group of factors has on the develop ment of the source. Any community is usually limited to a comparatively few available sources of water supply, and the selection of any source must take into consideration the factors enumerated under this head, if not from the standpoint of acceptance or rejection, then from the standpoint of nature and degree of treatment necessary to counteract the effects of such pollution factors as are found to exist. Some of the factors requiring consideration under this head are geological formations of the area, surface scour and wash, vegetable and animal growths, and contamination by human agencies. The geological formation of any area has much to do with the possibilities of pollution of water supplies. A tight clay soil offers much less probability of wastes from a pit privy percolating to a near by well than would a coarse gravel stratum. Fine, porous, sandy soils also act as natural filters and reduce the potential danger of pollution. On the other hand, cavernous limestone regions containing free underground channels where polluting wastes may be carried for long distances are highly dangerous. In fact the sewage from some cities in such regions is sometimes discharged into sinks. with unknown outlets. Many instances are on record where peculiar geological formations have been the direct cause of serious epidemics of water-borne diseases. Knowledge of the geological formation is also of value from the standpoint of mineral pollution of possible water-supply sources. Thus the underground waters of certain areas are strongly impregnated with sulphur, rendering such waters useless as sources of supply; other areas produce only highly saline waters, and still others have an abnormally high iron content. Even surface waters may be seriously affected by contamination with highly acid drainage from active or abandoned coal mines, or may be liable to be so contaminated if coal measures form a part of the geological strata. Surface wash also, plays a part as an active or potential source of pollution. High turbidities are mostly the effect of excessive surface scour, which brings to the stream a conglomerate mixture of polluting substances, including dangerous and offensive organic matter deposited on the watershed. Usually such pollution is highest at periods of high-stream flow, regardless of the increased dilution at such times. Flashy, quick-spilling streams with wide and sudden variations in discharge need, therefore, to be carefully examined when considered as sources of supply. Forestation is usually conceded to have a deterrent action on soil erosion, and is therefore of value. in the protection of watersheds, hence in the reduction of turbidity of streams. Vegetable and organic growths also play a part in the possible pollution of water supplies. Water coming from some sources may be so heavily seeded with vegetable organisms at times as to render it almost unfit for use by imparting disagreeable tastes and odors. Water from pine forests and peat swamps may be highly colored and have tastes that render it very objectionable. Certain microorganisms will also have a serious effect on tastes and odors if the source is not properly protected or if proper care is not exercised in storage and handling of certain classes of supplies. While these matters may not be regarded as polluting in the strict sense of the word, they are certainly factors that influence the use and popularity of the supply. Pollution by human agencies is the greatest and most serious source of potential and actual contamination of water supply. The ways in which such pollution may reach a source of water supply are almost infinite. The only safe way to eliminate the possibility of such pol lution is to remove the cause-that is, all human contact, both direct and indirect, with the source. Just in so far as this is done will the potential danger be reduced in degree. Attempts to follow this course have been made by many communities, notably those having untreated surface supplies. The watersheds have been entirely depopulated, many of them reforested, and are being carefully patrolled to prevent even accidental pollution. The results obtained by these measures have justified them. Other communities have for various reasons not been able to inaugurate such complete measures or have found other safeguards better adapted to particular conditions. There is practically, however, no unused surface source of supply of any size in this country that is not in potential, if not actual, danger of pollution by human agencies; and any contemplated source of this nature should be provided with suitable machinery for its protection or the elimination of the pollution before being used for drinking water. Where pollution of the source is of such nature as to be impractical of prevention, then measures for removal of this pollution by some artificial-treatment process must be provided to safeguard the consumers. Natural Safeguards. The detrimental effects of various agencies, both natural and arti ficial, on the quality of water supplies have been indicated above. In the grand balance of forces which nature attempts to maintain there is another set of factors actively engaged in reducing these detrimental effects-natural safeguards that are of immense value in assisting to restore such polluted water to its original quality. Some of the most important of these safeguards that may be employed are forestation, natural filtration, aeration, impounding or storage, and plankton activity. Forestation of extensive areas has a considerable retarding effect on the extent of the soil erosion and thus diminishes the amount of |