Going straight from eating three times per day to water fasting can wreck your motivation and keep you from sticking to your plan. It's much easier to start with a different kind of fast, such as an intermittent fast or an alternate-day fast.
If you want to stick to mostly liquids, but you're not sure you can make it with just water, try doing a liquid diet instead:
Flavor your water with lime or fruit infusions
Drink coffee or tea in addition to water
Consume bone broth or other broths to supplement your diet
Take multivitamins to keep up nutrient levels