Liquidity Plumbing

What this article does

The Fed sets the federal funds rate. We've covered that. But you might be wondering: how does the Fed actually MAKE rates be what it says they should be? When the Fed says "rates are now 4.25-4.50%", what's the mechanism?

The answer involves the financial system's plumbing — the bank reserves, the Treasury accounts, the repo markets, the money market funds — that quietly move trillions of dollars around overnight. Most retail investors never think about this layer. They probably shouldn't have to. But understanding it explains things that otherwise seem random:

• Why September 2019 had a sudden repo crisis
• Why the 2022-2024 inversion didn't tank markets the way history suggested
• Why "Net Liquidity" became a popular macro buzzword
• Why some Fed actions feel immediate and others feel like they vanish

This is article 6 of 9 in the Lighthouse foundation series. By the end:

• You'll understand bank reserves and why they matter
• You'll know what the Treasury General Account is and how it drains/adds liquidity
• You'll understand reverse repo and why $2.5 trillion sat there for a while
• You'll know what happened in September 2019 and why the Standing Repo Facility exists
• You'll understand Net Liquidity as a tracking metric (and its limits)

This is the wonkiest article in the series. Stay with me. The pieces click together by the end.

Bank reserves — the foundation

To understand liquidity plumbing, start with bank reserves.

Bank reserves are deposits banks hold at the Federal Reserve. As of late 2024, total US bank reserves were approximately $3.3 trillion. This is the foundation of the banking system's liquidity buffer.^[1] Bank reserves are deposits that commercial banks (Chase, Bank of America, etc.) hold at the Federal Reserve. Think of it as banks' own bank account at the Fed.

As of late 2024, total US bank reserves were approximately $3.3 trillion. That's the actual cash in the banking system that banks can move around freely — the foundation of liquidity.

When you deposit £100 at HSBC, HSBC doesn't keep that £100 in a vault. It keeps a small portion as physical cash for ATM withdrawals, and most of it goes into reserves at the central bank or gets lent out. Reserves are the truly liquid asset banks rely on for daily operations: settling payments with other banks, meeting customer withdrawals, satisfying liquidity requirements.

The amount of reserves in the system is largely controlled by the Fed. When the Fed buys Treasuries (QE), reserves go up. When the Fed lets bonds mature without replacement (QT), reserves go down. When the Treasury collects taxes and parks them at the Fed (TGA rises), reserves drain out of banks.

This is the central insight: liquidity flows. Money doesn't just sit. Every dollar in the financial system is somewhere, and "somewhere" matters.

The Treasury General Account (TGA) — the government's bank account

The US Treasury General Account (TGA) is the federal government's checking account at the Federal Reserve. When TGA balance rises (Treasury deposits cash), reserves drain from the banking system. When TGA falls (Treasury spends), reserves return to banks.^[2] The TGA is the US Treasury Department's checking account at the Federal Reserve. When you pay your federal taxes, the money ends up in TGA. When the government cuts a stimulus check or pays a contractor, the money flows out of TGA.

Here's the part that matters for markets: TGA flows directly affect bank reserves.

When TGA balance rises (Treasury collecting more than spending — like during tax season): Money flows from banks → into TGA. Bank reserves drain. The financial system has less liquidity.

When TGA balance falls (Treasury spending more than collecting): Money flows from TGA → into banks. Bank reserves grow. The financial system has more liquidity.

This is why end-of-quarter tax dates can be tight liquidity moments. April 15 and other corporate tax deadlines see massive payments to TGA, draining reserves. December year-end accounting can also stress liquidity.

The Treasury also moves the TGA balance deliberately for operational reasons. After the COVID stimulus packages, TGA briefly hit $1.8 trillion in 2020 — an unprecedented buffer. Through 2021, the Treasury drew that down, releasing trillions back into the banking system. That outflow into reserves was a major (if unappreciated) source of liquidity that helped support markets that year.

Reverse Repo — the parking lot

Now for the second drain on reserves: the Reverse Repo facility.

The Reverse Repo (RRP) facility lets money market funds and approved counterparties park cash overnight at the Fed earning a fixed rate. RRP balances peaked at $2.55 trillion in December 2022 and have since fallen as the cash redeployed elsewhere.^[3] The Reverse Repo (RRP) facility lets approved counterparties — primarily money market funds — park cash overnight at the Fed. They give the Fed cash, the Fed gives them Treasury collateral, and the next morning the trade reverses with a small fee.

The point: it's a place to put cash earning a fixed rate (set by the Fed, currently around 4.30%) when better options aren't available.

For most of 2022-2023, RRP balances were enormous — peaking at $2.55 trillion in December 2022. Why? Several factors:

1. Money market funds had massive inflows as customers chased higher rates than savings accounts offered 2. Few attractive alternatives — Treasuries were paying lower yields than RRP 3. Banks weren't paying up for deposits — they had ample reserves and didn't need more

So $2.5 trillion of cash sat parked at the Fed, technically counted as a liability of the Fed, draining it from the rest of the financial system.

When RRP balances fall (cash leaves the parking lot), it goes back into the banking system as reserves OR into Treasuries, both of which support markets. The drawdown of RRP from $2.5T to under $400 billion through 2023-2024 added significant liquidity even as QT was reducing the Fed's balance sheet. It's a major reason QT had less restrictive impact than expected.

Net Liquidity — the popular tracking metric

Net Liquidity is a popular macro indicator calculated as Fed Total Assets minus Treasury General Account minus Reverse Repo balances. Risk asset performance has historically correlated strongly with changes in this measure.^[4] Net liquidity is the popular metric that tries to summarise the above into a single tracking number:

Net Liquidity = Fed Total Assets − Treasury General Account − Reverse Repo

The intuition:

• Fed assets create reserves (positive contribution)
• TGA balances drain reserves (negative)
• RRP balances drain reserves (negative)

When net liquidity rises, banks have more reserves → easier financial conditions → typically supportive for risk assets. When it falls, the opposite.

It's not a precise model. Plenty of liquidity-affecting things aren't captured (foreign reserves, FX swap lines, repo facility usage, etc.). But for a single number you can track day-to-day, it's surprisingly useful.

You can build it yourself from FRED data:

• WALCL (Fed total assets) — weekly
• WTREGEN (Treasury General Account) — weekly
• RRPONTSYD (Reverse Repo) — daily

Sum the changes and you have a rough liquidity tracker.

The metric became famous in macro Twitter circles around 2022 when it correlated extremely well with S&P 500 movements — the QE/QT regime made reserves flows the dominant story. Correlation has weakened somewhat as RRP normalised, but it's still useful context.

The September 2019 repo crisis

The September 2019 repo market panic saw overnight repo rates spike to 10% (from a normal 2-2.5%) due to a confluence of corporate tax payments, Treasury settlement, and tight reserves. The Fed responded with emergency operations and eventually created the Standing Repo Facility in July 2021.^[5] To understand why the Fed cares so much about the plumbing, look at what happened in September 2019.

In normal times, overnight repo rates trade close to the federal funds rate — say 2-2.5%. That's banks lending each other cash overnight against Treasury collateral.

On September 17, 2019, repo rates spiked to 10% intraday. Ten percent. Overnight. That's not a market — that's a system in distress.

What happened? A confluence: 1. Corporate tax payments flowed to TGA on September 16, draining ~$100 billion in reserves 2. Treasury settlement of new bond issuance settled the same day, requiring more cash 3. Bank reserves were already tight — the Fed had been doing QT for two years 4. Quarter-end approaching — banks were preparing to shore up balance sheets

The combination meant there wasn't enough cash sloshing around to fund overnight repo at normal rates. Cash holders demanded higher rates. Cash needers were stuck.

The Fed responded immediately with emergency repo operations, eventually adding hundreds of billions in liquidity. They later expanded these into ongoing operations.

The lesson: the financial system runs on overnight liquidity. When reserves get too tight, the plumbing breaks before anyone realises a problem exists. The Fed needed a permanent solution to prevent recurrence.

The Standing Repo Facility

The Standing Repo Facility (SRF) was launched by the Fed in July 2021 to provide a permanent backstop on repo rates. Banks can borrow up to $500 billion overnight against Treasury and agency collateral.^[6] In July 2021, the Fed created the Standing Repo Facility (SRF) as a permanent answer to the September 2019 problem.

How it works:

• Banks and primary dealers can borrow up to $500 billion overnight from the Fed
• They post Treasury, agency, or MBS collateral
• They pay a rate slightly above the federal funds rate (currently about 4.50%)
• The next morning the trade reverses

The SRF effectively puts a ceiling on how high overnight repo rates can spike. If repo rates start rising sharply, banks just borrow from the SRF instead, which floods cash into the system and brings rates back down.

It's the financial system's pressure relief valve.

The SRF has been used relatively little so far — most of the time markets don't need it. But it's the kind of facility that proves its worth in moments of stress. The next September 2019 won't happen because the SRF would absorb the shock.

Why QT has been less restrictive than expected

Here's where everything connects: Quantitative tightening (QT) reduces bank reserves by letting Treasury and MBS holdings mature without replacement. Beginning June 2022, the Fed has reduced its balance sheet by approximately $2 trillion through QT.^[7]

Quantitative tightening began in June 2022. Since then, the Fed has reduced its balance sheet by about $2 trillion. That's a massive contraction — and based on the simple "QT reduces reserves" model, it should have caused major financial tightening.

It mostly didn't. Markets handled it gracefully. Banks didn't run into liquidity issues. The repo market stayed calm. Why?

Because the cash didn't disappear — it got reshuffled.

When the Fed's balance sheet shrank, the offsetting effect didn't come from bank reserves. It came largely from:

1. The TGA running down — Treasury was actively spending more than collecting through 2023-2024 2. The Reverse Repo facility draining — money market funds redeployed cash into Treasuries instead of RRP

The result: bank reserves stayed roughly stable around $3.0-3.4 trillion even as the Fed shrunk its balance sheet by $2 trillion. The QT impact was absorbed by the buffer of TGA and RRP, not by a reserve squeeze.

This is the crucial insight: QT's impact depends on what's in the buffer. If TGA and RRP are full, QT just drains those. If they're empty, QT directly impacts bank reserves and gets restrictive fast.

As of 2025, RRP is largely drained (under $400B). TGA has limited room to fall. The next phase of QT — if continued — would impact reserves directly. That's when QT actually starts being restrictive.

How to read liquidity flows

Practical guidance for using liquidity as a forecasting tool:

1. Watch RRP balances. When RRP is draining quickly, that cash is going somewhere — usually into Treasuries (suppressing yields) or into banks (boosting reserves). Both are positive for markets.

2. Watch TGA balances. When TGA is rising, reserves are draining. Persistent TGA build-up during QT is double tightening.

3. Watch the Fed's balance sheet weekly (H.4.1). Total assets minus TGA minus RRP gives you the rough liquidity picture.

4. Watch repo rates relative to the federal funds rate. When repo rates start trading above fed funds, reserves are getting tight. SRF usage is the next signal.

5. Don't overweight liquidity vs other factors. Liquidity is one input. Earnings, valuations, risk appetite, geopolitics all matter too. Net liquidity charts that "perfectly predict" market moves are usually overfit to recent data.

6. Quarter-end and year-end matter. Banks reduce balance sheet exposure for regulatory reporting at quarter-ends. December 31 has historically been the highest-stress liquidity moment of the year.

The Lighthouse takeaway

If you remember nothing else from this article, remember:

Bank reserves are the foundation of liquidity, currently around $3.3 trillion. The Treasury General Account (government's bank account) and Reverse Repo facility (cash parking lot for money funds) are the two main drains on bank reserves. Net Liquidity = Fed Assets − TGA − RRP is a rough but useful tracker. The September 2019 repo crisis showed what happens when reserves get too tight, leading to the Standing Repo Facility as a permanent backstop. QT has been less restrictive than expected because TGA and RRP drawdowns absorbed the impact rather than reserves. Once those buffers are empty, QT becomes much more restrictive.

The Lighthouse dashboard tracks Net Liquidity directly. The next time you see "Fed liquidity" in a macro discussion, you'll know what's actually being measured and why it matters.

The next article in the foundation series is Regime Change — because all the individual pieces (yields, spreads, liquidity, Fed policy) come together into different macro regimes that markets price differently.

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