Welcome to the forum!
Ditto to earlier comments. You might want to review the following search results:
. . . as well as the Fresh Water Systems forum:
Or Pumps sub-forum: https://www.airforums.com/forums/f445/
You may have dirty water in the water tank, so drain that, and fill with fresh city water, using a new potable water hose, and an inline filter:
Always use that kind of hose and filter both
for filling the tank, as well as for hooking up to city water.
After you have good water in the tank, turn the pump on and bleed all air from all the hot and cold faucets etc., including the outside shower and toilet. Then turn the pump on and off in rapid succession, in hopes of dislodging any grit caught in that previously referenced check valve. Very often this will solve your problem. If not a new pump may be in order.