 In the last case, there is an obvious safety issue, because many people do not expect to encounter more than the head of water above the drain when touching a drain.For example, in a recent case, a lifeguard went to the bottom of a pool to retrieve something and his hand got stuck because of the extra pressure from the pump.When there is a recirculating pump, the risk of suction consists of the head of water, plus the suction of the pump (up to a maximum of 1 atmosphere).