On Thursday, I had a consultation with Ken Foster who teachers the Permaculture class at Cabrillo College. He also owns Terra Nova Ecological Landscaping. I decided to hire a professional company to attach all the downspouts and tubes from the gutters to the water tanks to catch rain water. Ken recommended a strong and secure foundation for the tanks with a 2×12 frame and base rock. He suggested building the frame 5 ft. wide and 10 ft. long to accommodate 2 tanks that will weight over 4,200 lbs full of water.
I decided to look for another used water tank and found the perfect one (500 gallons) on Facebook Marketplace. It is black and an exact match to the other one which is green. We picked it up yesterday, and only had to drive 25 minutes to Santa Cruz. The tank is in new condition. What a lucky find!

Two 500 gallon tanks are the perfect fit for our space. I supposed we could keep connecting tanks if we are overflowing with water. The water can be used for fire safety, but realistically will water plants in our upper garden area through gravity flow and garden hose.