Water industry byelaws and your drains

Yes - it is a criminal offence to discharge fats, oils and grease into the public sewer, under Section 111 of the Water Industry Act 1991. Section 111 makes it an offence to throw, empty or turn into a public sewer (or allow to pass into it) any matter likely to interfere with the free flow of the sewer's contents, or to injure the sewer. Fats, oils and grease (FOG) fall squarely within this, because FOG poured or washed down the drain congeals and solidifies in the cooler sewer, building up and interfering with the free flow of wastewater (and forming blockages). So discharging FOG to the public sewer is an offence. The penalties are significant - a criminal offence with potentially costly fines (unlimited in the Crown Court), and the water company will typically also seek to recover the costs of clearing any blockage you caused. So putting grease down your drains is against the law, with real consequences. FOG must instead be kept out of the drains and disposed of properly. So yes - it is illegal to put grease down the drain into the sewer. This is general information, not legal advice.

The old water byelaws have largely been replaced by modern legislation and regulations, but the principle - that what connects to and discharges into the water and sewerage system is regulated - still applies. For water fittings and preventing waste and contamination of the water supply, the old water byelaws were replaced by the Water Supply (Water Fittings) Regulations 1999. For what you discharge into the public sewer (the relevant issue for kitchen drains and grease), the key law is the Water Industry Act 1991 - Section 111 of which makes it an offence to discharge matter likely to interfere with the free flow of the sewer, including fats, oils and grease. And the Building Regulations set drainage requirements (including grease separation for hot-food kitchens). So while the specific old byelaws may no longer be the operative rules, your drains and what goes into the sewer are still very much regulated - by the Water Industry Act 1991, the water-fittings regulations, and the Building Regulations. The practical rules for a kitchen (no FOG down the sewer, grease separation fitted) come from these. So the principle applies, under modern law rather than the old byelaws. This is general information, not legal advice; check current requirements.

For commercial hot-food kitchens, the Building Regulations expect the drainage to be fitted with a grease separator (complying with the relevant standard, such as BS EN 1825, sized and installed to the appropriate guidance) or other effective means of grease removal - so that grease is separated out of the wastewater before it reaches the sewer. So a compliant commercial kitchen is expected to have grease management (a grease trap or separator, or equivalent effective means) as part of its drainage, not just to rely on staff not pouring grease down the drain. This makes grease-management equipment part of proper kitchen drainage: the grease trap or separator intercepts the FOG in the wastewater, holding it back for proper removal and disposal rather than letting it pass into the sewer. So keeping FOG out of the sewer has two parts the rules expect - good practice (not putting grease and oil down the drain) and grease separation equipment (to catch the residual FOG in the wash water). A kitchen without effective, maintained grease separation risks discharging FOG (an offence) and causing blockages. So the Building Regulations expect grease separation for hot-food kitchens. This is general information, not legal advice; check the current requirements.

It causes flooding, cost and often closure - a serious, expensive event. When FOG goes down the drain it congeals and solidifies as it cools, building up inside the drains and sewer and eventually blocking them (often combining with other debris into solid blockages). A blocked drain backs up: wastewater has nowhere to go, so it backs up into your premises, flooding the kitchen or building with foul wastewater - a hygiene emergency, a mess to clean, and often a forced closure while it is dealt with. The costs are real: clearing a serious FOG blockage can cost thousands, and if the blockage is in the public sewer and you caused it, the water company can recover the clearance costs from you. Add the lost trade from any closure, the clean-up and any damage, and a FOG blockage is an expensive, disruptive event. So FOG blockages flood premises, cost thousands, can close you down, and may leave you with the water company's clearance costs - which is why keeping FOG out of the drains matters practically as well as legally. So a FOG blockage floods, costs and closes. This is general information, not legal advice.

Through good practice and effective, maintained grease separation. Good practice: do not pour grease and used cooking oil down the sink - scrape food and grease off plates and pans into the waste (not the drain), and dispose of used oil and grease properly (collected by a registered waste carrier, under the waste duty of care). This keeps the bulk of the FOG out of the drains in the first place. Grease separation: have effective grease-management equipment (a grease trap or separator, as the Building Regulations expect for a hot-food kitchen) fitted to the kitchen drainage, to catch the residual FOG that inevitably enters with the wash water - and keep it maintained, serviced and emptied so it keeps working (a neglected or overwhelmed grease trap stops catching grease). Keeping the kitchen clean also helps - deep cleaning removes built-up grease from the kitchen so less reaches the drains. So keep FOG out of the drains by not putting grease and oil down the sink, having and maintaining grease separation, and keeping the kitchen clean. So good practice plus maintained grease separation keeps FOG out. This is general information, not legal advice.

By catching and removing the grease before it reaches the sewer - keeping the drains flowing (avoiding blockages) and keeping you within the law (no FOG discharged to the sewer). Grease management (a grease trap or separator, plus good practice and proper disposal) intercepts the fats, oils and grease from the kitchen's wastewater and holds them back for proper removal and disposal, so they do not pass into the public sewer. That protects your drains and the sewer from the FOG build-up that causes blockages (flooding, cost, closure), and keeps you compliant with the law that makes discharging FOG to the sewer an offence. For it to work, the grease-management system has to be effective (properly specified and sized) and maintained (serviced and emptied so it keeps catching grease) - a neglected grease trap fails on both counts. Keeping the kitchen clean and grease managed also means less grease reaches the drains. So grease management protects your drains (no blockages) and your compliance (no FOG to the sewer) - which is why it, and its maintenance, matter. So grease management protects both your drains and your compliance. This is general information, not legal advice.