If you paid the LMRA entry fee, you can go to any campground within LMRA and use the facilities including water. Otherwise VoFSP visitor center has free potable spigot water and Overton Municipal Park has free fountain potable water.
At the Chevron Station on I-15. It is 6 miles from the BLM. The water is on the island in front of the street taco trailer. To the left of the gas ⛽️ pumps. There is also a propane filing station there.
There’s a huge gas station and fireworks store at the entrance right of the I-15 that has diesel, propane, potable water and a dump station. The camping location is about 5-6 miles east of it.
Hope that helps!