Mammoth Water Department - Pay Bill, Contact, Address & Services
Everything you need for Ynp-Old Faithful — serving 7,675 residents in Mammoth, WY.
7,675
Residents Served
153
Connections
Mon–Fri 8:00 AM – 5:00 PM
Office Hours
Mammoth Water Department Address
Yellowstone, WY 82190
Local Tip: Street parking near Mammoth municipal offices fills up fast before 10 AM. Arrive early if paying in person or drop your check in the after-hours payment box.
Mammoth Water Department Contact
Customer Service
(307) 250-2403
Office Hours
Mon–Fri 8:00 AM – 5:00 PM
How to Pay Your Mammoth Water Bill Online
Visit the Official Payment Page
Go to the Ynp-Old Faithful website. Look for the "Pay My Bill" or "Online Payments" section.
Enter Your Account Number
Find your account number on your paper bill (top-right corner). Enter it along with your last name or service address.
Choose a Payment Method
Select credit card, debit card, eCheck, or bank draft. eCheck is often free while cards may have a small convenience fee.
Confirm and Save Your Receipt
Review the total, submit payment, and save or screenshot your confirmation number. Payments usually post within 1-2 business days.
Quick Tip: Payments made before 3 PM usually post the same business day. Weekend and holiday payments process the next business day.
Mammoth Water Bill Payment Guide
Complete step-by-step payment instructions, accepted methods, billing tips, and more.
💡 Mammoth Insider Tips
Best Time to Call
Lines are shortest right when the office opens. Try calling at 8:00 AM on a Tuesday or Wednesday to skip the queue.
Save on Fees
Mammoth accepts eCheck payments at no extra charge. Card payments may add a $2-3 convenience fee per transaction.
Start, Stop, or Transfer Water Service
Start New Service
Moving into Mammoth? Contact Ynp-Old Faithful at least 3 business days before your move-in date.
✓ Valid photo ID required
✓ Proof of address (lease or deed)
✓ Deposit may apply for new accounts
Stop Service
Moving out? Request disconnection at least 2 business days ahead. You will receive a final bill.
✓ Final meter reading scheduled
✓ Forwarding address for final bill
✓ Deposit refunded within 30 days
Transfer Service
Moving within Mammoth? Transfer your existing account instead of closing and reopening.
✓ Same account number kept
✓ No new deposit needed
✓ Processing: 1-3 business days
Report Water Issues in Mammoth
Water Leak
Notice water pooling near the street or sidewalk? Call Ynp-Old Faithful immediately. Do not try to access the meter box yourself.
Sewer Backup
Call your utility before contacting a plumber. Mammoth will check the main line first at no charge if the issue is on their side.
Service Outage
No water? Check with your neighbors first. If the outage is widespread, call (307) 250-2403 for a restoration estimate.
Real-Life Tip: Take a quick photo or video of the issue before calling. It helps dispatch prioritize and gives the crew a head start before arriving on site.
Mammoth Water Billing & Fees
Mammoth Water Department FAQ
Visit the official Ynp-Old Faithful payment portal online. You can pay with a credit card, debit card, or eCheck. A guest pay option is available if you do not have an online account.
You can reach Ynp-Old Faithful at (307) 250-2403. The office is open during Mon–Fri 8:00 AM – 5:00 PM.
Ynp-Old Faithful is located at P.o. Box 168, Yellowstone, WY 82190.
Yes. Most municipal portals offer a one-time guest payment option. You only need your account number from a recent paper bill.
Many utilities accept past-due payments online, but reconnection timing varies. If your service is disconnected or scheduled for shutoff, call (307) 250-2403 before relying on portal timing.
Call Ynp-Old Faithful immediately at (307) 250-2403. For after-hours emergencies, most departments have a 24/7 hotline. Do not attempt to fix a main line break yourself.
Contact Ynp-Old Faithful at (307) 250-2403 at least 3 business days before your move date. Bring a valid ID and proof of address to start new service.