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Will the Dishwasher Harm the Septic System? - Septic Tank Maintenance and Cleaning Advice
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• Does a dish washing machine harm the septic tank or septic drainfield?
• What dishwasher detergents are best to use when a home is served by a septic tank and drainfield?
• What steps can be taken to minimize the impact of dishwasher use on a septic system?

Will the discharge from a home dishwashing machine into a private septic system harm the septic tank or drainfields? This document explains how to extend the life of the septic system by being careful about what goes into it.

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical review, content suggestions, critique are welcomed and are listed at "References."

This document is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems an online book on septic systems.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

A Guide to Home DISHWASHER Machines - and Septic Systems

DISHWASHERS - and Septic Systems

Does a dishwasher water volume overload and harm the septic system?

The volume of water from home dishwashing machine use should not be a problem with a normal septic system in good working order.

However as we discussed at "Washing Machines", in some conditions you should avoid emptying dishwasher discharge into the septic system:

• Drainfield capacity may limit dishwasher use: if the absorption system (leach field, drainfield) has limited capacity to absorb effluent
• A failing drainfield and use of dishwashers: if the absorption system is showing evidence of failure, such as effluent coming to the surface of the property or backing up into the building (nonetheless you need septic field investigation and repair)

Does dishwasher detergent harm the septic tank or septic system drainfield?

The volume of dishwasher detergent entering the septic system is so low as to be very dilute when it enters the septic tank, dilute enough that it is not going to harm the septic tank bacteria at normal levels of residential dishwasher use.

However many if not most dishwasher detergents contain phosphates or nonylphenol ethoxylate surfactants. Surfactants are what make detergents effective in lifting soil particles off of a surface (a dish in the dishwasher or a shirt in the washing machine).

Dishwasher detergents do not make a high level of suds inside the dishwashing machine. If you've ever made the mistake of putting normal dish soap into a dishwasher (as did this author) you know what a disaster will ensue - with sudsy soap overflowing out of the dishwasher and across the floor. Dishwashers rely on surfactants, high water temperature, and time spent spraying across the dishwasher contents to clean them.

Dishwasher & Laundry Detergents Containing Phosphates & Surfactants May Contaminate the Environment

Even if they don't kill off your septic tank or drainfield bacteria, surfactants and phosphates that run through a dishwasher ultimately enter ground water and surface water may also become contaminated.

Surfactants in dishwasher detergents (and from any source) are toxic to fish, basically suffocating them by interfering with the ability of the fish's gills to absorb oxygen from water.

Phosphates in dishwasher detergents pass through the septic system (or municipal wastewater treatment system) and enter surface water causing very high growth rates of algae. The algae growth, in turn, suffocates fish and other life in rivers, streams, lakes, and ponds. The rapidly growing "dead zones" at the edges of major water bodies around coastal areas of the U.S. and other countries are blamed on surface runoff that contains phosphates, (probably largely from agricultural use).

According to Cliff Davies, a U.S. EPA engineer reported in the New York Times the level of phosphates in dishwasher detergent has been significantly reduced since the 1970's. But Mr. Davies was unable to identify specific dishwasher detergent products or brands that were high in surfactants or phosphates, and the Times article reported that the U.S. EPA "Design for the Environment Program" which he administers does not track products that are problematic. The EPA does, however, list dishwasher detergent products whose manufacturers report to the EPA that they use the safest chemicals. The EPA does not perform tests to confirm the accuracy of product claims.

In sum, consumers who want to minimize their contribution to environmental pollutants by their choice of dishwasher or washing machine cleaning products may want to purchase products listed by the EPA's "Design for the Environment Program" but the listing designation does not appear to be supported by independent testing nor publicly available data. As of February 2009 it's the best we've got.

Install a Drywell to Handle Dishwasher Drainage to Protect the Drainfields from Overload

One option is to install a separate graywater system (greywater) or drywell to receive water from the dishwasher. If you are considering this step, consider connecting both dishwasher and clothes washer to a common drywell.

At some properties with very limited septic capacity, a large drywell may be installed to handle additional gray water from other building fixtures such as sinks and showers. See Drywells for additional information.

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SEPTIC SYSTEMS ONLINE BOOK
WHAT CAN GO INTO TOILETS & DRAINS?
NEVER FLUSH INTO SEPTICS
BETTER NOT TO FLUSH
HOUSEHOLD CHEMICALS
OTHER CHEMICALS
CHLORINE IN DRINKING WATER
CHLORINE IN SEPTIC WASTEWATER
DISHWASHERS vs SEPTICS
DRUGS INTO the SEPTIC TANK?
GARBAGE GRINDERS vs SEPTICS
REVERSE OSMOSIS CONCENTRATE DISPOSAL
TOILET TISSUE?
TOILET TISSUE TEST
WASHING MACHINES
WATER SOFTENERS
* NO FLUSH SUMMARY LIST

• New York Times: "When it Comes to Detergents, What's the Least Irresponsible Choice?", Julie Scelfo, New York Times, /26/2009 p. D7
• Drywells Home Buyer's or Owner's Advice

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More Information on Building Diagnostic Inspections and Repairs

• The Septic System Information Website home page for this topic


• Additives & Chemicals: Septic System Maintenance - Are they even needed? Are they even legal?
• Biomat Formation in the Septic System Drainfield Absorption System - what leads to drain field clogging and expensive drainfield repairs
• Buyer's Guide to Septic Systems - what to do when buying a home with a septic tank
• Cesspools Home Buyer's or Owner's Advice
• Cheating on Water Tests - (Chlorine in Wells and Septics) Testing Water for Real Estate Transactions - Water Test Cheating Warnings for Home Buyers and Home Inspectors
• Clogged Drain Diagnosis - is the problem the septic system or the Building drain system?
• Drywells Home Buyer's or Owner's Advice
• Contamination in Buildings how to test buildings for bacterial contamination from Sewage and Septic backup, remediation, & references
• Leach Field Inspection Procedure Septic Leach Fields - how to inspect and diagnose septic drainfield failures - what causes septic field failure?
• Maintenance: Ten Steps to Keeping a Septic System Working, suggestions from the U.S. EPA, edits and additions by DJF
• Septic Systems Inspection, Testing, & Maintenance Book - online textbook: how to inspect, maintain, repair septics
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Septic Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Sewage & Septic Backups and what to do about sewage spillage in buildings
• Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Tank Pumping Frequency Guide for Septic Tanks: When, How, What to Watch For when pumping or cleaning septic tanks
• Water Usage: Capacity: Determining Needed Septic Capacity - Typical residential water usage for people, appliances, and activities.
• What is a Septic System An Engineer's View & Septic System FAQ's

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