Hydro Hand (
Shown applications include removing dirt of a drained pool without the use of a deck brush by collecting the little remaining water and rolling it up until waist-level. It is enough to make a 10 courses-wide pool entirely clean. It is later shown that Hydro Hands can only control a fixed amount of clumps of water, as it becomes more difficult the more clumps an esper tries to control. It can be assumed that this is related to an esper's level. Furthermore, an esper that is at least level 3 can still control the water despite losing sight of it or if it is put in a container. Water being scattered on the ground renders it useless to the esper.
Incidentally, it seems that Hydro Hand powers are common in the Tokiwadai Middle School's swimming club.