What Is an Autofill System — and Why Does Your Pool Need One?

Why is your pool water level always low, even though you keep refilling it?
Could an outdated autofill system be silently wasting water — and money?

If you've ever walked outside and found your pool mysteriously low — or if you're refilling it more often than seems normal — you're not alone. These are common concerns for pool owners. And if you're in the planning phase of a new pool, understanding how to control your water level is more important than ever.

In this article, we’ll break down the two key components that control your pool’s water level — the autofill and the fill switch — and how today’s smart pool automation systems are helping homeowners eliminate waste, detect leaks early, and gain peace of mind.

What Is an Autofill System?

An autofill system is a device that automatically adds water to your pool when the water level drops too low — much like how a toilet tank refills after each flush.

Traditionally, this has been handled by mechanical float systems installed in a canister next to the pool. They’re simple in design but come with serious drawbacks.

Why mechanical autofills fall short today:

• Constant dripping or unnoticed leaks
  
  
• Underground plumbing issues
  
  
• Runaway filling that wastes thousands of gallons
  
  
• Outdated aesthetic (often hidden under unattractive plastic lids)
  
  
• No data or alerts to notify you of problems

What Is a Fill Switch?

A fill switch is the component that triggers the autofill system to turn on or off. In mechanical setups, it's usually a float. In smart systems, it’s often a sensor or timer even an irrigation celenoid, that activates based on pool usage and environmental conditions like evaporation. 

A faulty or inaccurate fill switch can overfill your pool — or fail to refill it altogether. Either way, you're risking equipment damage and a higher water bill.

Why Mechanical Autofills Create Risk

When I was a kid, the only way we knew the pool needed water was when the pump started screaming — a sound we later learned was called cavitation. That happens when the pump runs dry because the water level falls below the skimmer.

Cavitation significantly shortens the life of your pump.

Back then, we’d grab a hose or rely on those old-school autofills. But those systems came with a lot of hidden risks:

• Worn-out seals
  
  
• Continuous dripping or slow leaks
  
  
• No visibility into how much water is being added — or why
  
  

These systems work blindly and can secretly cost you money and harm your pool equipment.

Understanding Backflow and Plumbing Code Requirements

In any pool system, it’s essential to protect the potable (drinkable) water supply from contamination. This is where backflow prevention becomes critical — and it’s also a requirement under most local plumbing codes.

Backflow is the unwanted reverse flow of water — or a mixture of water and other substances — into the clean water supply. It can carry contaminants like chlorine, pool chemicals, and bacteria back into your home’s or community’s drinking water.

There are two main conditions that cause backflow:

• Backsiphonage: This occurs when negative pressure (a vacuum) in the water supply line pulls water from the pool system back into the drinking supply. Common causes include broken pipes or high water withdrawal rates.

• Backpressure: This happens when the pressure in your pool plumbing system exceeds that of the supply line, pushing pool water — and potentially contaminants — back into the potable source. Pumps, heaters, or elevation changes can all cause this.

To prevent contamination, plumbing codes require the use of backflow prevention devices, especially at points where cross-connections exist.

There are two types of backflow preventers, depending on the elevation of your pool relative to the water supply:

1. Atmospheric Vacuum Breaker (AVB) – Used when the pool is below the water source. It uses air pressure to prevent siphoning and is installed downstream of any valve that could close and trap water.
   
   
2. Pressure Vacuum Breaker (PVB) or Double Check Valve Assembly (DCVA) – Required when the pool is above the water source. These offer higher pressure tolerance and are more suited for systems with variable flow or automation.

Every pool system that connects to a drinking water supply must be equipped with a properly installed backflow preventer — not just for legal compliance, but to protect your family and your neighborhood from serious water quality risks.

The Smart Solution: Pool Water Automation

Today’s automated pool systems integrate water-level control with real-time tracking and intelligent alerts — all accessible from your smartphone or tablet.

Smart autofill technology gives you control and insights mechanical systems never could.

Key benefits include:

• Setting water level thresholds and refill limits
  
  
• Tracking historical usage and evaporation trends
  
  
• Getting alerts if water usage spikes (a key indicator of leaks)
  
  
• Sharing data with your pool technician for faster troubleshooting
  
  

This level of automation means your pool runs more efficiently, safely, and sustainably — while also protecting your investment.

Why You Should Upgrade Now

If you're considering installing a pool or already have an older autofill system, now is the ideal time to look into smarter solutions.

Autofill systems are only effective when they’re accurate — and monitored.
If your current setup is overfilling or hiding a slow leak, it's silently costing you time, money, and water.

Upgrading to a smart autofill system allows you to

• Catch issues early — before they become expensive
  
  
• Prevent water waste, especially in drought-sensitive areas.
  
  
• Extend the life of your pool equipment through better protection.

Take Control of Your Pool’s Water Use

Now you understand what autofill systems and fill switches do, how they fail, and why modern automation is the solution.

If you’ve dealt with inconsistent water levels, surprise water bills, or pump failures — you’re not alone.

Consider upgrading your pool with a smart automation system that gives you control, efficiency, and peace of mind.

Since 2008, J Designs has helped homeowners modernize their pools with technology that protects their investment and conserves resources. Check out our next article: Are Pools a Waste of Water?