Green house questions are absolutely welcome here. We also have a green house forum if you prefer to use that.
Heat is a big issue in greenhouses. I try to keep my hoop houses under 95° F. Most days in the summer they are between 85-90°. I do that with a combination of ventilations, fans and shade cloth.
Your plan sounds reasonable but the effect will be temporary. If your hoop house is hot the ground won't stay cool for long. And while you don't say how cold your water is, be careful if it is really cold as you wouldn't want to shock the plants with frigid water.
I would focus on ventilation, fans and shade cloth. You should have windows and vents to allow air to circulate. And fans to pull out the hot air. You can purchase solar powered fans if you don't have power in your green house.
Shade cloth will help prevent your greenhouse from getting too hot by limiting the amount of sun that gets into it. Shade cloth comes in a variety of densities from 10% to 100%. That varies the amount of light that gets thru the cloth. The crops you grow and the climate in your area will determine the density you need. I'm at a high altitude in New Mexico. I grow mostly greens and vegetables and I use 60% shade cloth. Be sure to purchase the correct density for your needs and area.