Yes, Hoddesdon has a real flood risk, though it is concentrated in particular areas. A small part of the town is in the highest-risk river zone. When rainwater runoff is counted as well, about one postcode in six has a high-risk flag. Allowing for climate change makes the river zones bigger. Most homes are fine, and the ones that aren't are close to the water.
The town runs along the River Lea, the Lee Navigation and the New River. About 4% of Hoddesdon's postcodes are in the Environment Agency's Flood Zone 3, which is the highest-probability river and sea zone. Another 7% are in Flood Zone 2, the medium-probability band just outside it. The two zones don't overlap, so between them they cover about one postcode in ten. The Lea and the Lee are the same river with two spellings, and the water ignores both.
Rainwater that can't drain away does not follow the river zones at all. That is why it is counted in the wider postcode measure further down this page and not here. The Environment Agency's records give a sense of the history. It holds 118 recorded flood events for the area, and about 9% of postcodes are inside a historic flood outline. The most recent recorded event was in December 1968, when a main river overflowed a channel with no raised defences. In the 1620s, Sir Marmaduke Rawdon gave the town its first public water supply. The rivers have kept supplying more than anyone asked for.
The Environment Agency also models how the flood zones change with climate change. On that version, about 13% of Hoddesdon's postcodes fall inside the river and sea zones. That is the zone map with an allowance for wetter decades, so it is worth reading for any home you plan to keep for a long time.
For insurance, a home in Flood Zone 3, or close to the edge of it, can cost more to cover, carry a higher excess, or need a specialist insurer. Get a quote for the exact address while your offer is still being negotiated, not after exchange. "Close to the towpath" reads well in a property listing, but an insurer reads the same words very differently.
The postcode measure is wider. It flags a postcode if any one of several flood indicators applies, including rivers, the sea and surface water. On that basis, about 17% of Hoddesdon's postcodes have at least one high-risk rating, 22% have at least one medium rating and 47% have at least one low rating. A postcode only needs one flag to be counted, so these shares are bigger than the river zones and measure something different.
Counting homes gives a clearer picture. The Environment Agency's river and sea mapping lists 2,105 properties in Hoddesdon postcodes with some level of risk. Postcodes with no risk at all are left out. Of those properties, 307 are at high risk, 315 at medium risk, 525 at low risk and 296 at very low risk. Of the high-risk group, 132 are homes.
Flood defences change some of this. In the Environment Agency's model of the most likely flooding, about 4% of postcodes fall inside the extent with no defence in the way, and about 3% are inside it even though a defence is present. "Defended" only means the model includes a defence at that spot. It does not mean the defence keeps the water out every time, and some of those defended postcodes are still within the modelled flood area.
Flood risk is Hoddesdon's weak point: most of the town is dry, but the homes near the Lea carry enough risk to need a careful look at the paperwork.