Ask your government: is glyphosate monitored in drinking water?
Most countries choose not to. New Zealand doesn't. Glyphosate is increasingly considered the world's most significant environmental toxin. It's not a long stretch to consider that our residues are increasing. Yet there is no formal testing of glyphosate in New Zealand in the ESR Survey of Pesticides in Groundwater. Glyphosate is increasingly detected in surface and groundwaters.
Why isn't glyphosate frequently monitored?
1. It requires a separate expensive residue test. Normally a standard multi-residue test is conducted to evaluate pesticide residues in water. Glyphosate is much more difficult to detect.
2. Out dated, privately held science keeps it from being considered toxic by the major regulatory authorities. As a result, the World Health Organisation (WHO) hasn't even bothered to set a minimum standard for glyphosate in drinking water. As a result, countries that adhere to WHO standards don't test for the active chemical in Roundup (let alone the other ingredients in the full formulation). Somewhat astonishingly, the WHO simply isn't looking at recent publicly released science to make it's decisions.
'The half-life of glyphosate in water and soil is longer than previously recognized. In field studies, the half-life of glyphosate in soil ranged between a few days to several months, or even a year, depending on soil composition. Studies have shown that soil sorption and degradation of glyphosate exhibit great variation depending on soil physical, chemical, and biological properties. The risk of long-term, incremental buildup of glyphosate contamination in soil, surface water, and groundwater is therefore driven by highly site-specific factors, and as a result, is difficult to predict and costly to monitor.'
Why glyphosate and Roundup? It's the most commonly used pesticide in the world. It has been found to leach out of soils into rivers, streams, and into groundwater.  Yet glyphosate/Roundup is rarely tested as it is a separate test from the common multi-residue pesticide analysis, and is therefore expensive to test for, requiring additional treatment than other chemicals.
The 2011 World Health Organisation Guidelines for drinking water quality have agreed not to set a 'formal guideline value' - ie. established minimum requirements, for glyphosate in drinking water.  The reason? Glyphosate occurs 'in drinking-water at concentrations well below those of health concern'. But this is because of outdated science:
On page 374 the WHO Guidelines detail 'a health-based value of 0.9 mg/l can be derived based on the group ADI for AMPA alone or in combination with glyphosate of 0–0.3 mg/kg body weight, based upon a NOAEL of 32 mg/kg body weight per day, the highest dose tested, identified in a 26-month study of toxicity in rats fed technical-grade glyphosate and using an uncertainty factor of 100'.  WHO does not give a study author, perhaps it is G.R. Lankas who, with G.K. Hogan carried out the 1981 study which establishes the ADI for New Zealand, Australia, Canada and Europe.  No small feat for two unpublished Monsanto funded studies.
This private (hidden by confidentiality agreements) 26 month study is thirty-three years old and provided by Monsanto. There is not even a study author noted. The WHO bases their justification on the international recommended level of Roundup - our daily exposure for the rest of our lives - on this single ancient study.
This decision has a domino-like affect as WHO member countries adopt guideline values do not appear to present risk.
We have modern public domain research demonstrating danger at current levels of exposure. This is excluded from consideration. System failure.
Detection of glyphosate in groundwater is increasing:
'WHO received a communication that research by the Geological Survey of Denmark and Greenland had found glyphosate levels in groundwater five times higher than the EC/EU allowed level for drinking-water. The use of glyphosate in Denmark has doubled in the last five years.' 
The European Commission, US EPA and the WHO increased the permitted residue levels 6-fold on wheat and cereals in 2006 - from 5 mg/kg to 30 mg/kg. This is due to higher residues from desiccated cereals - wheat being sprayed up to 7 days before harvest in order to mature it quickly in climates with less predictable rainfall.
Drinking water legislation in Europe is derived from the EU Drinking Water Directive which sets minimum standards for various substances in water. European legislation is the most cautious. For any individual pesticide the maximum allowed at any time is 0.1 µg/l (parts per billion) and the total for all pesticides must not exceed 0.5 µg/l. These standards are based on a highly precautionary approach with values close to zero and are not related to actual toxicity of the pesticides. 
'Glyphosate use in the United States increased from less than 5,000 to more than 80,000 metric tons/yr between 1987 and 2007...... Glyphosate and AMPA were detected frequently in soils and sediment, ditches and drains, precipitation, rivers, and streams; and less frequently in lakes, ponds, and wetlands; soil water; and groundwater.' Battaglin et al 2014.
Environmental Protection Agency limits (maximum contaminant level) for glyphosate in
'The tolerances listed in 40 CFR §180.364(c) are for the combined residues of glyphosate and its metabolite AMPA resulting from the use of irrigation water containing residues of 0.5 ppm following applications on or around aquatic sites, and are established at 0.1 ppm. The Agency's Office of Water has established a maximum contaminant level (MCL) of 0.7 ppm for glyphosate per se in drinking water (FR Notice: Vol. 57, No. 138, page 31776, dated July 17, 1992)'. 
'The NPDWR established an MCLG and an MCL of 0.7 mg/L. The Agency developed the MCLG based on an RfD of 0.1 mg/kg/day and a cancer classification of D, not classifiable as to human carcinogenicity.'  This is how the EPA appear to arrive at tolerances:
(a) RfD of 0.1mg/kg/day:
US IRIS database: RfD of 0.1mg/kg/day is based on an unpublished 1981 Monsanto study. 2 studies are given: MRID 0081674 Schroeder, R.E.; Hogan, G.K. (1981) Unpublished Monsanto/Bio/dynamics & MRID 00105995 Street 1982 Unpublished Monsanto)
Sometimes an RfD of 2mg/kg/ bw/day is quoted, Rodwell et al 1980 (Unpublished Monsanto).
(b) The cancer classification of D is based on the following Monsanto studies P.13 :
Lankas, G.R.; Hogan, G.K. (1981) (Unpublished Bio/dynamics/Monsanto)
Stout, L.; Ruecker, F. (1990) (Unpublished, Monsanto).
McConnel, R. (1985) (Unpublished Bio/dynamics/Monsanto)
The permitted drinking water levels for Roundup by the W.H.O. and US e.p.a. are established by using 30 year old, private Monsanto studies to declare low toxicity.
Mom's Across America commissioned a report and revealed: The levels found in the breast milk testing of 76 ug/l to 166 ug/l are 760 to 1600 times higher than the European Drinking Water Directive allows for individual pesticides'. 
And New Zealand?
To quote an ECAN employee 'We do not routinely test drinking water because this is the responsibility of the water supplier. I do not know if any public drinking water wells have been tested for glyphosate, but I do not suspect there will be many, if any, because it is not a parameter for which a limit is set in the NZ Drinking Water Standards.'
The NZ Drinking Water Standards are based on the WHO guidelines for drinking water quality. Using the glyphosate example alone it is evident that NZ standards are not safe enough.
So we don't test, and we should. Particularly in our cereal and horticultural regions. If we were to apply it more practically, regional authorities should be testing for pesticides most utilised in their regional areas. But this isn't happening either.
Myers J P et al (2016). Concerns over use of glyphosate-based herbicides and risks associated with exposures: a consensus statement. Environmental Health 15(19). DOI 10.1186/s12940-016-0117-0. https://ehjournal.biomedcentral.com/articles/10.1186/s12940-016-0117-0
 Vereecken, H. (2005) Mobility and leaching of the glyphosate: a review. Pesticide Management Science Vol. 61 pp 1139-1151.
SURVEY OF GLYPHOSATE AND AMPA IN GROUNDWATERS AND SURFACE WATERS IN EUROPE - UPDATE 2012. H. Horth (Independent Adviser, Water Quality and European Policy & Legislation).
 'For glyphosate, the USGS developed the method and you can only get glyphosate and its metabolite with the method so it is a lot of work and expense for 2 analytes. For cost considerations, we don’t test for it. So far, the USGS has only detected glyphosate metabolites in a few wells. To the best of my knowledge, they haven’t seen it in surface water. ' USDA Scientist
 WHO Guidelines for Drinking Water Quality. Fourth edition. World Health Organization. ISBN 978 92 4 154815 1 Page 374.
 The portion of the private Monsanto study the public are permitted to see. WHO document WHO/SDE/WSH/03.04/97 Glyphosate and AMPA in Drinking Water.
Bio/Dynamics Inc. (1981a) A lifetime feeding study of glyphosate (Roundup technical) in rats. Unpublished report prepared by Bio/Dynamics Inc., Division of Biology and Safety Evaluation, East
Millstone, NJ. Submitted to WHO by Monsanto Ltd. (Project No. 410/77; BDN-77-416).
Groups of Charles River Sprague-Dawley rats (50 per sex per dose) were fed technical glyphosate in their diets at dose levels of about 0, 3, 10 or 32 mg/kg of body weight per day for 26 months. Survival, appearance, haematology, blood biochemistry, urinalysis and organ weights were not changed. Slight growth retardation during part of the study was noted in the high-dose males. The incidence of interstitial cell tumours in testes showed a statistically significant increase (incidences: 0/50, 3/50, 1/50 and 6/50; historical control range: 3–7%) (Bio/Dynamics Inc., 1981a). This finding, in itself constituting evidence of a carcinogenic effect in rats, should be judged in light of the absence of an effect at much higher dose levels in the more recent 2-year study in rats (see below). This is also valid for the slight growth retardation. The NOAEL was 32 g/kg of body weight per day, the highest dose tested (Bio/Dynamics Inc., 1981a).
 Lankas, G.R.; Hogan, G.K. (1981) A Lifetime Feeding Study of Glyphosate (Roundup Technical) in Rats: Project No. 772062. (Unpublished study received Jan 20, 1982 under 524-308; prepared by Bio/dynamics, Inc., submitted by Monsanto Co., Washington, D.C.; CDL:246617-A; 246618; 246619; 246620; 246621). MRID 00093879
§171-4 (f): Nature and Magnitude the Residue in Drinking and Irrigation Water P.30:
00039377 (Monsanto unpublished), 00039381 (WSU/Monsanto unpublished), 00077227 (Monsanto unpublished), 00077228 (Monsanto unpublished), 00077229(Monsanto unpublished), 00077230 (Monsanto unpublished), 00077231 (Monsanto unpublished), 00077232 (Monsanto unpublished), 00077233 (Monsanto unpublished), 00077234 (Monsanto unpublished), 00077235 (Monsanto unpublished), 00077236 (Monsanto unpublished), 00077237 (Monsanto unpublished), 00077238 (Analytical Biochemistry Labs/Monsanto unpublished), 00077301 (Monsanto unpublished), 00108173 (Monsanto unpublished).
 Moms Across America and Sustainable Pulse: Glyphosate Testing Full Report: Findings in American Mothers’ Breast Milk, Urine and Water. April 7 2014.