Unless you have the unfortunate need to own petroleum based (plastic), silk or preserved plants, every plant (even drought tolerant) need water. New plants are especially needy when it comes to water. The more established a plant becomes, the less water it requires, however care must be taken. Most people overwater their plants which will kill a drought tolerant plant just as fast as a lack of water.
One way to tell if you are overwatering is to watch for wilting of the leaves and squeeze a leaf to check for excessive moisture. A properly watered plant should have crisp leaves.
Another reason your plants might be dying is that you aren’t planting your plants in the right location. Check to see where your native plants prefer, i.e., moisture, available sun light, salt tolerance, organics in the soil. Sometimes plants just die. Newly installed plants are more susceptible to transplant shock, but that isn’t all, critters (insects, rodents, dogs, etc.) will do their part to bring about your plants untimely demise.
Usually it is more than 1 thing that bring about the demise of a plant especially tough drought tolerant plants. So take heart, it isn’t always your lack of green thumb that brings about the death of your beautiful plants.