As noted above, 3–5 million gallons of water are needed to frack a well. This water can be pumped from surface water or groundwater sources, and recycled flowback can be used to supplement and even dramatically reduce these withdrawals. In situations where water is plentiful, such withdrawals may do little if any damage. Concerning surface water, during low-flow periods, water withdrawals could raise pollutant concentrations or temperature, or even simply reduce flow so as to damage aquatic habitat. In addition, even during higher-flow periods, there can be tension between the desire to withdraw water from sources as close to the well pad as possible to save costs and drawing water from larger surface water bodies or water bodies with less ecological significance that are farther away.