By Nidal al-Mughrabi and Dawoud Abu AlkasCAIRO/GAZA, July 21 (Reuters) - In pre-dawn darkness, Ibtisam Al-Helou leaves her tent on Gaza's seafront on a daily search for fresh water. The Mediterranean lies only a few steps away, but the water she needs to cook, drink and wash will mean a trek across Gaza City.Setting out before the heat rises to the scorching 33 degrees Celsius (91 F) of midday, the 40-year-old mother of three makes her way through shattered neighbourhoods where word has spread that water might be available.