exchangers. The temperatures of the recirculating water, piping and heat exchange surfaces determine if and where minerals will precipitate from the recirculating water. Often a professional water treatment consultant will evaluate the make-up water and the operating conditions of the cooling tower and recommend an appropriate range for the cycles of concentration. The use of water treatment chemicals, pretreatment such as water softening, pH adjustment, and other techniques can affect the acceptable range of cycles of concentration. Concentration cycles in the majority of cooling towers usually range from 3 to 7. In the United States, many water supplies use well water which has significant levels of dissolved solids. On the other hand, one of the largest water supplies, for New York City, has a surface rainwater source quite low in minerals; thus cooling towers in that city are often allowed to concentrate to 7 or more cycles of concentration. Since higher cycles of concentration represent less make-up water, water conservation efforts may focus on increasing cycles of concentration. Highly treated recycled water may be an effective means of reducing cooling tower consumption of potable water, in regions where potable water is scarce. Maintenance Clean visible dirt & debris from the cold water basin and surfaces with any visible biofilm (i.e., slime). Disinfectant and other chemical levels in cooling towers and hot tubs should be continuously maintained and regularly monitored. Regular checks of water quality (specifically the aerobic bacteria levels) using dipslides should be taken as the presence of other organisms can support legionella by producing the organic nutrients that it needs to thrive. Water treatment Besides treating the circulating cooling water in large industrial cooling tower systems to minimize scaling and fouling, the water should be filtered to remove particulates, and also be dosed with biocides and algaecides to prevent growths that could interfere with the continuous flow of the water. Under certain conditions, a biofilm of micro-organisms such as bacteria, fungi and algae can grow very rapidly in the cooling water, and can reduce the heat transfer efficiency of the cooling tower. Biofilm can be reduced or prevented by using chlorine or other chemicals. A normal industrial practice is to use two biocides, such as oxidizing and non-oxidizing types to complement each other's strengths and weaknesses, and to ensure a broader spectrum of attack. In most cases, a continual low level oxidizing biocide is used, then alternating to a